Washington - The Republican Party will take control of both chambers of the US Congress for the first time in eight years this week, setting the stage for power struggles on issues from health care to the environment that could define the final two years of President Barack Obama’s term.The Republicans, who took control of the Senate from the Democrats in last November's elections and expanded their majority in the House, began laying down markers for legislative battles ahead. In their sights are Obama's signature 5-year-old health care law, his recent executive actions on immigration sparing millions from deportation, and environmental and business regulations.Sending a message that he's still relevant heading into the final two years of his presidency, Obama has made a series of high-profile presidential moves, including steps toward normalising relations with Cuba, that infuriated Republicans. No matter what the Republican Congress passes, Obama retains the power to veto legislation, an action he's taken only twice in six years.As mandated by the Constitution, Congress was to convene at noon local time.Despite the confrontations certain to loom ahead, Republican leaders and the White House have indicated there is potential for cooperation on issues like trade, tax reform and infrastructure spending. The challenge for leaders of both parties will be facing down pressure from their more ideological members.The leader of the House, Speaker John Boehner, has seen his efforts to forge compromises thwarted in recent years by lawmakers aligned with the ultraconservative tea party movement. But his hand is considerably stronger this year as a result of the sweeping Republican electoral triumph. The party will hold 246 House seats in the new Congress, to 188 for the Democrats, the biggest Republican majority in nearly 70 years.Boehner's prospects of getting a new term as speaker appeared secure despite grumblings from tea party-aligned dissidents.The election of a speaker will be the main event as the new Congress convenes. Tea party-backed Reps Louie Gohmert of Texas and Ted Yoho of Florida put themselves forward as challengers to Boehner, and roughly a dozen Republicans have announced they will oppose Boehner's election. But that was far short of the number needed to place his election in jeopardy.Many Republican lawmakers dismissed the challenge as a needless distraction at a moment when the party should be celebrating its new majorities and showing voters it can lead."It's time to put all this silliness behind and move on," said Rep Phil Roe of Tennessee. "We're on probation. If we don't perform ... [voters] can make a pivot in a heartbeat."For Republicans, their day of empowerment is being marred somewhat over a controversy over revelations that the House's No 3 Republican, Majority Whip Steve Scalise, spoke to a white supremacist group 12 years ago.The White House waded into the furore on Monday, saying it's up to Republicans to decide whether Scalise will retain his job and who the party has in leadership "says a lot about who they are".White House Press Secretary Josh Earnest repeatedly said Scalise once described himself as "David Duke without the baggage", referring to the former leader of the white supremacist Klu Klux Klan. A reporter for the New Orleans Advocate newspaper said Scalise made the remark to her as he was starting out in the Louisiana Legislature nearly 20 years ago.In the Senate, Kentucky Senator Mitch McConnell's ascension on Tuesday to the post of Senate majority leader was automatic following his approval by rank-and-file Republicans late last year. McConnell, who had been the Senate minority leader, faced criticism from tea party supporters over his role in brokering a bipartisan spending deal that ended a government shutdown in 2013. But he survived a tea party primary challenge last year and went on to handily win re-election to his Kentucky seat in the general election.Despite their intra-party leadership struggles, Republicans are showing their potential to advance an agenda, pointing toward a swift veto showdown with Obama over the long-stalled Keystone XL oil pipeline from Canada to Texas.The legislation, opposed by environmental groups and many rank-and-file Democrats, passed the House but died in the Democratic-led Senate late last year. Now, Republican leaders intend to push the bill through the House late this week, and appear to be close to having enough votes to clear it through the Senate as well, given the Republican pickup of nine Senate seats in the elections.While Obama has not said if he will reject the measure, White House spokesperson Earnest outlined a series of concerns with the measure before adding, "I'm not prepared at this point to issue a veto threat related to that specific piece of legislation."Obama might also face pressure from his party's liberal wing if he tries to work out a deal with congressional Republicans to fast track approval of the Trans-Pacific Partnership, a trade deal that 12 nations are trying to negotiate.Senate liberals, led by Democratic Senator Elizabeth Warren and independent Senator Bernie Sanders, have declared opposition to the trans-Pacific trade deal contending it would benefit global corporations at the expense of American workers.