Hours after supporters of the bill to approve the much-delayed Keystone XL pipeline made it the first piece of legislation introduced in the new Republican-controlled Senate, the White House said for the first time that Obama would veto it.

That set up the first of what is expected to be many confrontations over energy and environmental policy between Obama and the Republican-controlled Congress.

Republicans condemned the veto threat, which came at the same time they were savoring the fruits of their victory in last November’s elections and speaking optimistically about bipartisan compromises in the two years ahead.

The Republicans seized control of the Senate from the Democrats and expanded their majority in the House of Representatives in the midterm elections, an outcome certain to complicate the final two years of Obama’s Presidency as he seeks to cement his policies on health, the environment and immigration. Still, both sides have identified areas where compromise is possible, including trade.

“I’m really optimistic about what we can accomplish,” said Sen. Mitch McConnell of Kentucky, moments after he was recognized as leader of the new Republican Senate majority.

At the other end of the majestic Capitol building, Rep. John Boehner of Ohio easily won a third term as House speaker despite an attempt by ultraconservative tea party-backed dissidents to topple him.

The 25 votes cast against Boehner by fellow Republicans was a historically high number for a sitting House speaker, but his critics were so disorganized that they spread their votes among nine potential replacements.

Still, it served notice that the ultraconservative faction that has been a thorn in Boehner’s side for the past two sessions of Congress will not fall quiet during the new one despite the Republicans’s bigger control.

Seeking unity despite the internal party dissension, Republicans moved swiftly to advance the Keystone XL pipeline, setting votes in a Senate committee and on the House floor for later this week.

Boehner said the 114th Congress would make passing legislation to “develop more North American energy” among its top priorities, adding, “We invite the president to support and sign these bipartisan initiatives into law.”

But even before Boehner spoke, White House Press Secretary Josh Earnest said, “If this bill passes Congress, the president wouldn’t sign it.” He said the measure would undermine a review process underway by the administration.

Moments after highlighting the possibility for compromise, Boehner issued a statement saying Obama had sided with the “fringe extremists” in his own party in opposing the pipeline.

Said McConnell: “The President threatening to veto the first bipartisan infrastructure bill of the new Congress must come as a shock to the American people who spoke loudly in November in favor of bipartisan accomplishments.”

The bill is sponsored by 54 Republicans and six Democrats — enough to overcome procedural hurdles to gain Senate approval but short of the two-thirds majority needed to overturn a presidential veto.

The pipeline project, which is highly important to Canada’s government, would move tar sands oil from Canada 1,179 miles (1,900 kilometers) south to Texas refineries on the Gulf of Mexico. Supporters say it would create jobs and ease American dependence on Middle East oil.

A government environmental impact statement also predicted that a pipeline would result in less damage to the climate than moving the same oil by rail.

Critics argue that the drilling itself is environmentally harmful and the pipeline would provide few permanent jobs, while any leaks could threaten the aquifer in the agricultural heartland.

They said much of the Canadian crude would be exported with little or no impact on America’s drive to reduce oil imports, which have already been greatly reduced because of record U.S. oil production.

The events spilled out rapidly on a day that offered a glimpse of the political forces at work in an era of divided government — the intraparty struggle among House Republicans, the coordination that Republicans in both houses chambers in pursuing a conservative agenda and the blocking power of a Democratic president.

Republicans now have a 54-46 majority in the Senate and took 246 of the 435 seats in the House, the most in more than 60 years.

Republicans were eager to turn to an agenda tailored to suit conservatives. They have signaled plans to write a budget that eliminates federal deficits in 10 years or less and to pass an overhaul of the tax code as well as try and reduce federal regulations they say are stifling job creation.

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Associated Press writers David Espo, Erica Werner, Nedra Pickler, Charles Babington, Stephen Ohlemacher, Deb Riechmann and Andrew Taylor contributed to this report.