After a packed overseas trip that included some icy encounters with Vladimir Putin and high-stakes talks with China's Xi Jinping, President Obama is back in Washington -- where a new cluster of confrontations awaits. 

While the president was away, a former adviser's unguarded comments about ObamaCare fueled Republican calls to dismantle the law; details leaked about his controversial plans for overhauling immigration via executive action; and lawmakers pushed anew to force approval of the Canada-to-Texas Keystone pipeline. 

On top of that, there is a Nov. 24 deadline for nuclear negotiations with Iran, and questions are surfacing within the administration about whether to overhaul U.S. policy toward Syria. 

The president and Congress will face all these issues and more over the next several weeks, as both race to finish work before the next -- Republican-controlled -- Congress is sworn in come January. 

Most immediate will be a Senate vote set for Tuesday on the Keystone XL Pipeline. The issue re-emerged on Congress' agenda thanks in large part to the Senate runoff election in Louisiana, where Democratic Sen. Mary Landrieu is fighting to keep her seat next month. In a bid to flex her D.C. clout, she sponsored a bill green-lighting Keystone. 

On "Fox News Sunday," South Dakota GOP Sen. John Thune called it a "cynical attempt to save a Senate seat in Louisiana." 

Nevertheless, Landrieu's election rival, GOP Rep. Bill Cassidy, put forward the same bill in the House, which easily approved it on Friday. The Senate vote on Tuesday could send the Keystone bill to Obama's desk for the first time -- forcing him to decide whether to sign it or wield his veto pen. 

Landrieu, though, would need to corral 60 votes to secure passage. All of the Senate's 45 Republicans are expected to support it, and aides say commitments from Democratic senators bring them to 59 -- meaning they're still pushing to find one more "yes" vote before Tuesday. 

Environmentalists continue to oppose the project and Obama has given indications he would veto the legislation, deferring to a long-running State Department review process. 

Meanwhile, a steady stream of videos from a former ObamaCare architect has caused major headaches for the Obama administration, just ahead of the weekend's second launch of enrollment. The comments from Jonathan Gruber, an MIT economics professor, were dug up in videos from the last several years, and show him gloating about how the authors of the Affordable Care Act took advantage of the "stupidity" of Americans. 

Obama, asked about the video over the weekend, told reporters that Gruber "never worked on our staff" and "expressed an opinion that I completely disagree with in terms of the voters." 

He said Gruber's comments are "no reflection on the actual process." 

Gruber, though, did work with the administration through a six-figure contract with the Department of Health and Human Services. 

And his remarks have fueled Republican criticism of the law, as the party prepares to assume the majority in Congress come January and push anew to repeal the law. Some have already suggested holding hearings on Gruber's remarks. 

As these controversies roil Washington, Obama returned Sunday night from a trip to China, Burma and Australia. When Obama first set off for the Asia-Pacific, both the White House and Republicans were suggesting that the GOP's decisive takeover of the Senate in the midterms could pave the way for bipartisan breakthroughs. But just two weeks after the election, that optimism largely has faded, making it increasingly likely that Washington will churn through two more years of gridlock. 

Republicans attribute the swift shift in tone largely to Obama's plans to move forward with executive actions on immigration that potentially could shield from deportation about 5 million immigrants who are living in the United States illegally. The president has pledged to announce the measures before year's end; he could act shortly after returning to Washington. 

The incoming Senate majority leader, Mitch McConnell of Kentucky, has warned that such executive actions would "poison the well" with the new Republican-led Senate and could prevent the GOP from working with Obama on other potential areas of agreement. 

Republican leaders are considering what to do if Obama presses ahead. More conservative members want to use upcoming spending bills to block the president, but that could set the stage for a showdown for another partial government shutdown. 

Obama said that possible threat would not dictate his timing in flexing his powers. He said his main concern "is getting it right." 

On Monday, Senate Democratic leaders including Majority Leader Harry Reid wrote to Obama voicing support for using "well-established executive authority to improve as much of the immigration system as you can." 

On Iran, Obama faces a deadline to reach a final agreement in sensitive nuclear negotiations. High-level talks in Oman last week failed to yield a breakthrough, potentially setting Obama up for a choice between pursuing another extension or abandoning the diplomatic effort. 

The president has asked the Congress to start debating a new authorization for his airstrike campaign against Islamic State militants in Iraq and Syria, though he expects the legislative effort to pick up next year when Republicans take control of the Senate. The debate comes as Obama faces questions from within his own administration, including from Defense Secretary Chuck Hagel, about the effectiveness of the military operation, particularly in Syria. 

Hagel said in a memo to White House national security adviser Susan Rice that Obama needed a clearer strategy for dealing with embattled Syrian President Bashar Assad. 

White House officials have denied that Obama is undertaking any formal review of his Syria strategy and the president said Sunday that he was not considering ways to oust Assad. 

Also on the agenda: getting the Senate to confirm his nominee for attorney general, federal prosecutor Loretta Lynch. The White House is not pushing for that in the postelection session of Congress, and says the president is leaving the timing up to Senate leadership. Democrats are reluctant to push a fight with an empowered GOP over the process and White House officials say they are confident Lynch will be confirmed even with Republicans in control. 

The Associated Press contributed to this report.