Following President Obama’s ambitious executive order on immigration — unprecedented not in subject matter but in scope and ambition — we are left to pick through the wreckage of law and precedent.

Obama’s action was a substitute for legislation — imposed precisely because legislation he favored did not pass. So what issues might have been raised during the legislative debate Obama preempted?

There is the matter of arbitrariness. Obama’s defense of his action is sweeping and unqualified. We are not a nation that “accepts the cruelty of ripping children from their parents’ arms.” Unless, of course, they arrived less than five years ago. A moral rule is apparently bounded by a bureaucratic line. And an appeal intended to put Republicans on the defensive also puts Hillary Clinton on the spot. One possible news conference question: “Madam Secretary, if an American president has the unilateral power to remove people from the shadows, why not people who arrived during the Obama years?”

There is also the matter of implementation. The U.S. Citizenship and Immigration Services processes about 4 million cases of all kinds each year. Now as many as 4 million applications — involving documentation of the arbitrary five-year limit — will be added over an indeterminate period of time. The office, which is currently overwhelmed, has six months to prepare for the onslaught. Opportunities for fraud and exploitation will certainly multiply. Will the lines for services provided to legal immigrants lengthen? An actual legislative debate might have clarified these challenges, particularly in light of the administration’s Obamacare and Veterans Affairs debacles.

The American political system not only lacks action; it lacks deliberation. On immigration, Obama has provided the first by circumventing the second — and provided a precedent for other presidents to avoid deliberation on other matters. During campaign-like events, Obama has made a strong case for immigration reform legislation, employing arguments that could have been made (and were) by George W. Bush. He has not made a case for short-circuiting the legislative process, except for noting that Congress has not acted in the way he wants, on the time line he prefers. It is an Augustinian ploy, made from a Jimmy Carter-like political position.

But — and this is perhaps the most significant conjunction of its kind since Kim Kardashian’s — Obama’s action shows the power of even a weakened president to influence a public debate. After all of the important legal, practical, political and procedural objections to Obama’s executive order, he has called attention to a fundamentally sympathetic group of human beings caught in an unjust and unworkable system. People who come to America to construct a better life, sometimes at great personal cost and risk, are not common criminals, even when they lack documentation. They (and all of the rest of us) deserve an immigration system that honors both the rule of law and human dignity. Our current one does not.

Obama’s willful revision of that law has problems of its own. It falls short on visas for high-tech workers. It provides no path to citizenship. In the most cynical (and most likely) interpretation, it uses undocumented workers in a vast political ploy.

But, no Republican running for president — or, at least, no Republican with serious prospects of actually becoming president — can simply say that the group that Obama has registered will be summarily deported. This would be impractical, immoral and politically self-destructive. Any future Republican proposal for comprehensive immigration reform will need to include a provision that deals with this humanitarian concern. Obama’s action — however currently controversial — will not be entirely undone.

This is already evident in the serious Republican response to the executive order — from a strengthened and disciplined Republican congressional leadership — which has focused on confronting Obama’s overreach rather than scapegoating people his action is designed to help. Former Florida governor Jeb Bush placed his opposition to Obama’s power grab within the context of a call for comprehensive reform — the only position that allows the GOP to confront its long-term demographic challenges.

Obama’s action on immigration creates a situation similar to health care. Obamacare was passed in a partisan march, implemented incompetently and sold to the public (as we know from professor Jonathan Gruber) in a deceptive fashion. But Republicans running for president will still need to propose a market-oriented alternative for the people currently getting health coverage under Obama’s plan.

This may be Obama’s very mixed presidential legacy. His methods are controversial, divisive and sometimes disturbing, and they often failed; his goals have shifted the American political debate.

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President Obama on Sunday responded to Republican critics who have accused him of acting like an emperor with his recent immigration actions, repeating his challenge for Congress to “pass a bill.”

Meanwhile, Republican leaders spent the weekend trying to craft a viable political response to the president’s immigration moves as outrage among the most conservative GOP elements continued to boil.

During an interview that aired Sunday on ABC’s “This Week,” Obama said he would prefer to address immigration issues through bipartisan legislation. “It didn’t happen, because [Speaker John A. Boehner] didn’t call the bill for a vote in the House,” he insisted.

Host George Stephanopoulos challenged the president on 2012 campaign comments that suggested he did not have authority to stop deportations on his own.

“What is absolutely true is that we couldn’t solve the entire problem and still can’t solve the entire problem,” Obama replied. “But what we can do is to prioritize felons, criminals, recent arrivals, folks who are coming right at the border, and acknowledge that if somebody has been here for five years, they may have an American child or a legal permanent resident child — it doesn’t make sense for us to prioritize them.”

Sen. Ted Cruz (R-Tex.) is shown speaking in Washington Sept. 26. (Manuel Balce Ceneta/AP)

Sen. Ted Cruz (R-Tex.), a potential 2016 presidential candidate, recommended blocking the consideration of Obama’s federal nominees, outside of national security posts, and using the budgetary process to thwart the implementation of the administration’s changes to immigration policy.

“In my view, the majority leader should decline to bring to the floor of the Senate a nomination other than vital national security positions,” Cruz said on “Fox News Sunday.” “The second big check we have got is the power of the purse, and we should fund, one at a time, the critical priorities of the federal government.”

Cruz’s efforts could have consequences for the White House, potentially holding up the confirmations of attorney general nominee Loretta Lynch and others, as well as for congressional Republican leaders, who have not endorsed Cruz’s approach.

By challenging Sen. Mitch McConnell (R-Ky.), the soon-to-be majority leader, Cruz in effect sent a warning shot to the GOP leadership, which remains largely undecided about what exactly they will do to counter the president.

Cruz signaled that the responses floated by some members of the party’s brass — including possibly suing the administration and rescinding appropriations for immigration programs once the GOP takes control of both chambers next year — may not be aggressive enough for those conservatives spoiling for showdowns that would stall the White House at every turn.

Beyond Capitol Hill, conservative leaders pleaded with congressional Republicans to consider articles of impeachment against Obama and weigh using budget maneuvers to confront the president, even if it leads to the second government shutdown in two years.

“It is idiocy for Republican leaders to constantly repeat that they are taking the power of the purse and impeachment off the table,” said Richard Viguerie, a longtime conservative activist. “Those are the very tools the Constitution bestows upon Congress to rein in a lawless president.”

House GOP aides said they expected Boehner to hold off on announcing any bills or other actions until after members return to Washington following the Thanksgiving holiday.

But in phone calls and e-mails, top Republicans on Saturday tried to advance an appropriations package that would also extend government funding past the Dec. 11 expiration date, signaling the leadership’s eagerness to avoid a fiscal standoff over immigration in the remainder of the lame-duck session.

Sen. Susan Collins (R-Maine), a member of the Senate Appropriations Committee, said appropriators “remain engaged in negotiations with our House counterparts.”

“The worst option would be to force a government shutdown,” Collins said. “That would hurt a lot of people and undermine our message that we can govern responsibly. I’m confident that if we pass an appropriations bill, we can come back next year when we start the budget process again and put limitations on particular [immigration] agencies that would curb abuses in those areas.”

Rep. Michael McCaul (R-Tex.) said Sunday that Republicans don’t plan to shut down the government.

“We are not going to shut the government down, but we are going to shut down the president and his actions as it pertains to granting amnesty to 5 million people,” McCaul, who heads the House Homeland Security Committee, said on CBS’s “Face the Nation.”

Also under consideration is an expansion of the lawsuit against the Obama administration’s use of executive authority that was filed Friday. The lawsuit focuses on the Affordable Care Act, but Boehner has broached the idea of adding an immigration challenge to the complaint, according to House Republicans close to him. At a luncheon last week, he told allies that litigation would almost certainly be part of the GOP playbook on immigration. But this lawsuit has already encountered challenges, and it could take months or years to be settled.

In the ABC interview that aired Sunday, Stephanopoulos questioned Obama’s defense that Republican presidents have used executive action to address immigration, noting that previous administrations exercised that authority only after Congress passed bipartisan bills.

Obama argued that those presidents implemented actions that went beyond the legislation that Congress had passed.

In his follow-up, Stephanopoulos asked whether the next president should be able to use executive action to ignore tax laws and effectively lower taxes.

“The reason that we have to do proprietorial discretion in immigration is that we know that we are not even close to being able to deal with the folks who have been here a long time,” Obama said. “Everybody knows, including Republicans, that we’re not going to deport 11 million people.”