Defiant Obama says he won't bend to GOP

WASHINGTON (CNN) -- A defiant Barack Obama dives into what could be a defining period of his presidency this week, after repeatedly enraging Republicans from afar during his Asia tour.

Obama faces showdowns with the GOP over immigration, the Keystone XL pipeline and his drive for a nuclear deal with Iran, all of which have huge consequences for his political legacy.

Far from being chastened by the Republican capture of the Senate, Obama is setting out to prove he is no lame duck and can still set the agenda.

But the GOP insists the mid-terms gave them a share of power in Washington, and believe Obama risks usurping his authority and even the constitution with his bold new strategy.

Obama drawing lines on immigration, climate change

Obama chose a highly symbolic setting to set the tone for two final White House years in which he will face a unified Republican Congress.

Side-by-side in Myanmar with the world's most famous dissident, Obama refused to bow to what Republicans regard as the capital's new political "reality."

On the veranda of the lakeside villa from where Aung San Suu Kyi faced

down a junta, Obama said he had long warned House Republicans he would use executive power to reform the US immigration system if they failed to.

"That's gonna happen. That's gonna happen before the end of the year."

The president doubled down in Australia on Sunday, before boarding Air Force One for home, saying he would be derelict in his duties if he did not act.

"I can't wait in perpetuity when I have authorities that at least for the next two years can improve the system," he said.

White House officials have not said when Obama will wield his executive powers in a move that could remove the threat of deportation for millions of undocumented people. But they say it will be soon.

While Obama was abroad, post-election tensions escalated sharply on Capitol Hill as happy talk from both sides about working together quickly ebbed away.

Senior aides dispute the idea the elections were a referendum on the President and say Obama is at his best when he is on "offense" and believe that's what Americans want to see.

So, as he trekked through Asia, Obama rattled Republicans almost every day.

He surprised everyone with a new climate deal with China that the GOP slammed as costly and "ridiculous." He popped up on video to discuss new Internet regulations that may spark another row. He refused to budge on approving the Keystone XL pipeline to take oil from Canada to the Gulf Coast. He may veto a bill on the project that Congress is expected to pass this week.

While in Asia, the president debunked the idea that the plan, opposed by environmentalists in his political base, would create lots of jobs and lower gas prices.

Obama says he still wants to work with Republicans on tax reform and infrastructure spending bills. But it looks like he has decided that he won't compromise his legacy priorities to get that done.

GOP promises retribution, but avoids specifics

Republicans are fuming over Obama's go-it-alone attitude since voters handed the GOP the Senate and expanded its majority in the House.

"We'd like for the president to recognize the reality that he has the government that he has, not the one he wishes he had," said the next Republican Senate Majority leader Mitch McConnell.

Republican Sen. Lindsey Graham warned Obama could spark a backlash over immigration.

"If he goes it alone he is going to run into the ire of the American people," Graham said, though said Congress also had a responsibility to act.

Republican Senate leadership member Roy Blunt warned however that Obama will eventually have to play ball, or he will end up with Republican bills he doesn't like.

"At that point, his choice is to sign it or veto it."

Republican leader John Boehner said his goal was to stop the president from violating his oath of office and the constitution.

"There are things he is just not going to get."

Republican anger is however masking a serious problem the party has yet to resolve : how to hit back at what it sees a presidential power grab.

Other than warning that Obama would "poison the well" for future cooperation, GOP leaders won't say whether they will use pending federal funding bills as leverage.

That route led to a damaging government shutdown for which the GOP paid a heavy political price last year.

One response could be to pass a series of short term funding measures, that keep administration priorities in limbo and maximize Republican leverage.

House Republicans could also chose to expand the lawsuit they have already lodged against Obama alleging he usurped his authority in implementing Obamcare. Conservative columnist Charles Krauthammer stirred buzz on Friday by declaring executive action on immigration would even be an "impeachable" offense.

GOP leaders are already braced for pressure from the right for a tangible and not merely symbolic reflex when the president acts.

"If the president moves forward and does his executive action, the Republicans have no choice but to respond," said Dan Holler, communications director of Heritage Action for America, a conservative non profit group.

"That response needs to be legislative. The vehicle that makes most sense is denying funding for the activity that they say is unconstitutional and inappropriate."

Obama's strategy could divide Republicans

Holler's point reflects a secondary benefit some Democrats see in Obama's strategy --- it will cause a big political headache for Republican bosses.

Obama's immigration move is certain to ignite a firestorm of grass roots conservative anger. That will in turn pile pressure on rank-and-file Republican House members who campaigned for office slamming what they see as an imperial president.

Some conservative lawmakers were already skittish at leadership warnings that it might be impossible to repeal Obamacare with a Democratic president in the White House.

Nothing worries Republicans in deeply conservative districts more than the prospect of a primary challenge, and many simply cannot afford not to mount the kind of rowdy response to Obama which will rock Boehner's restive caucus.

Several House Republicans are arguing that it's time to quickly get to work on holding hearings and drafting an immigration bill to demonstrate their party has its own reform ideas, and is not just about blocking the president's policies.

"Ultimately we all know we've got to deal with this problem, so why not start dealing with the problem - even though it's the lame duck, even though you're not going to get anything through to final passage," Idaho Republican Rep Mike Simpson told reporters Friday.

"Now we could start showing some seriousness that we're going to address this problem."

Executive orders on immigration will also detonate as the 2016 presidential race dawns, trapping Republicans between the party's activist base and a desire to engage Hispanic voters vital to GOP White House hopes.

Republicans are also adamantly opposed to the nuclear deal with Iran which could emerge from down-to-the-wire talks in Vienna starting this week and are threatening to upend it with new sanctions.

Obama appears to reject the idea Republicans have a mandate for change at all. He stressed in his post-election news conference that two thirds of Americans did not even vote and he was "the guy who's elected by everybody."

But he knows a tough political fight looms and reflected Friday on the contrast between polarization at home and the welcome he gets on his travels.

"You are always popular in somebody else's country. When you're in your own country, everybody is complaining."

CNN's Senior Congressional Producer Deidre Walsh contributed to this story.