WASHINGTON - Republicans are assuming full control of Congress for the first time in eight years in a day of pomp, circumstance and raw politics beneath the Capitol Dome.

They planned to move swiftly Tuesday toward a veto showdown with President Barack Obama over the Keystone XL pipeline, summoning unity despite a tea party-backed effort to unseat House Speaker John Boehner of Ohio.

As mandated by the Constitution, Congress was to convene at noon.

In the Senate, with Vice President Joe Biden presiding, Mitch McConnell of Kentucky was to automatically ascend to majority leader following his approval by rank-and-file Republicans last year.

McConnell and Boehner both were to deliver remarks on their chamber's floors as they positioned themselves for two years of clashes with Obama.

First, Boehner had to survive his election as speaker - the main event on any opening day's agenda. Tea party-backed Reps. Louie Gohmert of Texas and Ted Yoho of Florida put themselves forward as challengers to Boehner, and at least 10 Republicans announced they would oppose Boehner.

But that was far short of the number needed to place his election in jeopardy, and many lawmakers dismissed the challenge as a needless distraction at a moment when the party should be celebrating new majorities and showing voters it can lead.

"It's time to put all this silliness behind and move on," said Rep. Phil Roe, R-Tenn. "We're on probation. If we don't perform ... (voters) can make a pivot in a heartbeat."

Nor did any of the rebels predict they would succeed in toppling the 65-year-old Boehner. Instead, they said the current high command wasn't conservative enough.

For his part, Yoho said the initial goal of the Boehner challenge is to force the leadership contest past one ballot, so there could be a serious discussion about change.

"It's either a vote for the status quo or a new direction for the Republican Party," Yoho told CNN in an interview Monday morning. "This is the time for a new beginning. It's time for new leadership."

Yoho said the Boehner leadership team, among other things, hasn't given rank-and-file GOP members sufficient time to consider legislation before calling for a vote.

Virginia Rep. Dave Brat, who defeated former Majority Leader Eric Cantor in a primary last summer, said the Republican leadership has "strayed from its own principles of free market, limited government, constitutional conservatism."

Two years ago, Boehner faced similar criticism, and sweated out his election to a second term.

His hand is considerably stronger this year after the Republicans' sweeping electoral triumph. The party will hold 246 House seats in the new Congress, to 188 for the Democrats, the biggest GOP majority in nearly 70 years.

The intra-party leadership struggle underscored the political peril facing Republicans as they looked ahead to two-house control of Congress. Yet the evident ability to pass the Keystone pipeline legislation showed their potential to advance an agenda.

Votes in a Senate committee and on the House floor were scheduled for later this week on the pipeline, which passed the House but died in a Democratic-led filibuster in the Senate late last year. Now, Republicans appear to have more than enough votes to clear it through the Senate as well, given the Republican pickup of nine seats in the elections.

While Obama has not said if he will reject the measure, White House spokesman Josh Earnest outlined a series of concerns with the pipeline before adding, "I'm not prepared at this point to issue a veto threat related to that specific piece of legislation."

But Republicans stand ready to cast the measure as a bipartisan jobs bill of the type that should be signed into law.

"There's a lot we can get done together if the president puts his famous pen to use signing bills rather than vetoing legislation his liberal allies don't like," McConnell said late last year.

Earnest was less ambiguous about another issue.

Referring to an assertion by a Louisiana reporter, he said Rep. Steve Scalise of Louisiana, the third-ranking House GOP leader, had once described himself as "David Duke without the baggage." Earnest also said Scalise's presence in the leadership of House Republicans "says a lot about who they are."

Scalise spoke more than a dozen years ago to a white supremacist organization founded by Duke. The lawmaker said recently the appearance was a mistake, and said he condemns the group's views.