NEW YORK (AP) — President-elect Donald Trump is facing an early test with fellow Republicans over U.S. 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 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’s transition team announced Monday that his choice to head the Department of Homeland Security is, as expected, Gen. John Kelly. Kelly is a former commander of U.S. Southern Command with “unique insight into some of the challenges the United States faces at its southern border,” the announcement said.

Trump planned 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 U.S. election on behalf of Trump, raising red flags among lawmakers concerned about the sanctity of the U.S. voting system and potentially straining relations at the start of Trump’s administration.

In a wide-ranging interview with “Fox News Sunday,” Trump dismissed those concerns as little more than partisan griping. “I think the Democrats are putting it out because they suffered one of the greatest defeats in the history of politics in this country. And frankly, I think they’re putting it out. And it’s ridiculous,” Trump said.

The incoming president said he did not necessarily oppose calls from President Barack Obama for an inquiry into the 2016 campaign hacking but said it should not be solely focused on a single culprit.

“If you’re gonna to do that, I think you should not just say ‘Russia.’ You should say other countries also, and maybe other individuals,” he said. The White House has said the probe would focus on any breaches by other countries along with hacking committed in previous elections.

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