A day after he won reelection and Republicans retook the Senate, Sen. Mitch McConnell (R-Ky.) left no doubt that the edge-of-disaster showdowns with President Obama that have marked the past four years would be a relic of the past.

“Let me make it clear: There will be no government shutdowns and no default on the national debt,” McConnell said in a valedictory news conference in Louisville.

Less than two weeks later, that pledge is facing its first big test. A series of deadlines will force the incoming Senate majority leader to either find a way to keep his word or else get dragged into the same cycle of showdowns that has yielded few conservative victories and a lot of public anger.

Rather than starting the new year with a clean slate, McConnell is increasingly likely to begin by dealing with a pile of leftover government funding bills. McConnell and House Speaker John A. Boehner (R-Ohio) hoped that those spending bills could be finished by mid-December and provide funding for the rest of 2015, enabling the newly emboldened Republican majorities on both sides of the Capitol to challenge Obama on a host of issues.

But McConnell could be tripped up by the same conservative forces that have undercut Boehner since he became speaker in 2011.

The issue this time is Obama’s expected executive action to overhaul the nation’s immigration system. Obama is likely to allow millions of illegal immigrants to remain in the country without fear of deportation — a move opponents refer to as “executive amnesty” — along with other changes.

Staunch conservatives, led by Sen. Jeff Sessions (R-Ala.), the incoming chairman of the Budget Committee, have urged McConnell and Boehner to fight back by allowing only a short-term budget bill that would keep government agencies open until early next year.

These conservatives believe that once Republicans hold both chambers of Congress next year, they can force Obama to accept a budget bill that would prohibit him from implementing his executive order on immigration. Some Republicans, like Sessions, have said every option should be on the table, including a shutdown of the government over the issue.

The path McConnell takes between confronting Obama on immigration while keeping the federal government open could go a long way toward determining how he will serve as majority leader.

If McConnell can find a way forward, he could establish a foundation from which House and Senate Republicans can unite around conservative ideas without further damaging their party’s image.

If he blunders, however, the days of brinkmanship could return with a vengeance, and the government could once again be shut down. That could provide a devastating blow to Republicans, hurting their chance to win back the White House and hold on to their relatively slim Senate majority in 2016.

McConnell’s advisers are worried enough that by Friday evening they were circulating a memo showing how damaging last year’s shutdown was to the Republican Party — an effort designed to counter conservatives who point to this month’s triumphant election as proof that the shutdown did little damage.

The memo showed that in Gallup polling from late 2012 until this month, voters have barely wavered on Democrats, with favorability ratings for the party moving between 45 percent to today’s 42 percent.

Republicans held steady just a couple of points lower through 2012 and most of 2013 — until the 16-day shutdown of the federal government in October 2013. In just a few weeks, the McConnell chart shows, Republican favorability plummeted 10 points. It has taken a year for it to climb back to where it was before the shutdown.

In his reelection campaign, McConnell touted his role as the broker who reopened the federal government and who cut other deals that averted fiscal calamities, including possible default on the Treasury’s $17 trillion debt in 2011 when the government was up against its borrowing limits.

After that 2011 deal, McConnell told The Washington Post that the debt ceiling was “a hostage that’s worth ransoming,” citing a package of more than $2 trillion in spending cuts that accompanied the legislation.

Those days, he now believes, should be over. With control of both chambers and the ability to put legislation on the Senate and House floors, GOP leaders want to dissuade members from engaging in “hostage” situations over the debt ceiling and other issues.

“We have the opportunity now to pass a budget, which has to do with how much you’re going to spend. So I think we have other mechanisms that were unavailable to us with the previous configuration of the government, and I think that’s a pretty important tool,” McConnell said the day after the elections.

His advisers also want to use the same approach to push back on the immigration order that Obama is likely to issue. Given the heated response from so many Republicans, Senate GOP leaders now expect to pass a short-term funding bill into next year.

Once they have full control of Congress, according to some GOP advisers, the leadership hopes to sell the rank-and-file on making the fight part of the normal legislative process. The House and Senate judiciary committees, with oversight of immigration, would hold hearings and pass legislation to overturn Obama’s executive order, sending it to the floor for debate and handling the confrontation in a more orderly fashion.

That scenario would allow Congress to then approve the government funding bills for the remainder of fiscal 2015 and avoid any major showdown.

The problem with that approach is that Obama would almost certainly veto any legislation that countered his action on immigration.

Another problem is that it would require Republicans to embrace so-called regular order, an idea that has been out of favor with the hardest charging conservatives on Capitol Hill and their tea party allies outside government. In this case, they think regular order would almost certainly lead to a stalemate with Obama on immigration, while allowing a budget to pass.

Sessions has led the charge in the Senate to pass a short-term funding bill and use a potential shutdown as leverage to restrict funds needed to implement the president’s expected order. The most conservative House members are rallying around that plan as well.

That is putting pressure on Republicans who are usually reliable supporters of the McConnell-Boehner approach, particularly those who could face a primary challenge from the right.

Sen. Mike Crapo (R-Idaho), who has worked with Democrats on fiscal matters and is up for reelection in 2016, took a hard-line approach to the issue last week in an interview with a conservative news outlet. He wants to use the federal spending bills as leverage, although he would support letting the vast majority of agencies get their funding while Republicans withhold money related to immigration and border security.

“If the president and Congress got into a disagreement, we could move ahead with proper policies in other appropriations bills and continue to resist the president in the specifics of the one bill which was topical,” Crapo told Breitbart News.

Such a showdown could lead to a partial shutdown, which McConnell also is desperate to avoid. Back in September 2013, House GOP leaders thought they had a plan that would allow their members to vote against funding the health-care law but keep the government open, a tricky parliamentary move that staunch conservatives rejected and that ultimately failed.

Now, McConnell is trying the opposite — old-fashioned legislative debate on issues without the threat of fiscal calamity. Asked three times Thursday about a shutdown, he issued almost verbatim his declaration from Louisville: “We will not be shutting the government down.”