President-elect Donald Trump is facing an early test with fellow Republicans over US relations with Russia, as lawmakers seek to investigate a CIA assessment that Russia interfered in the November election and issue warnings over the incoming president's potential pick for secretary of State. Trump said on Sunday the recent CIA assertion that Russian hacking had sought to help his candidacy was "ridiculous," and he praised ExxonMobil CEO Rex Tillerson, who has emerged as the leading contender to lead the State Department. But two key Senate Republicans — John McCain of Arizona and Lindsey Graham of South Carolina, a leading Trump critic — joined with two Democrats in seeking a bipartisan investigation into the Kremlin's activities during the election. And McCain, the party's 2008 presidential nominee, questioned whether Trump should nominate Tillerson, citing the executive's longstanding business ties with Moscow. "It's a matter of concern to me that he has such a close personal relationship with Vladimir Putin," McCain said of Tillerson. "And obviously they've done enormous deals together." In an interview with CBS' "Face the Nation," McCain said, "That would color his approach to Vladimir Putin and the Russian threat." Russia expects to figure prominently at the start of a week in which Trump is expected to name more members of his Cabinet, which also has vacancies in the departments of Energy, Agriculture and Veterans Affairs. Trump is also planning a news conference on Thursday to outline how he intends to separate himself from his sprawling business enterprise. During his campaign, Trump weathered turbulent relations with fellow Republicans but has since forged a more united front with GOP lawmakers since his November victory over Hillary Clinton. The CIA recently concluded with "high confidence" that Russia sought to influence the US election on behalf of Trump, raising red flags among lawmakers concerned about the sanctity of the US voting system and potentially straining relations at the start of Trump's administration. — AP