Moscow has denied USA intelligence agencies' conclusion it meddled in the campaign to try to tilt the election in Trump's favor.
"There is no collusion - certainly myself and my campaign - but I can always speak for myself and the Russians - zero", he said at a joint press conference with Colombian president Juan Manuel Santos.
House Oversight Committee chair Jason Chaffetz, a senior Republican, said the memo and related documents "raise questions as to whether the president attempted to influence or impede the FBI's investigation".
On Thursday morning, Trump tweeted: "With all of the illegal acts that took place in the Clinton campaign & Obama Administration, there was never a special councel (sic) appointed!"
"I don't think I'm in a position to give any advice to President Trump".
Amash is a member of the hard-line House Freedom Caucus who has already has called for an independent commission to investigate. It is expected to include scrutiny of Trump's fired national security adviser, Michael Flynn, as well as his former campaign manager, Paul Manafort, and two former advisors, Carter Page and Roger Stone, and their contacts with Russian officials.
It would be significant if more Republicans began to talk about impeaching the president, as the party holds a majority in both chambers of Congress. A small number of Democrats also have mentioned impeachment.
Reporters pressed the Colombian president to comment on Trump's "America First" policy and the proposed southern border wall, but Santos sidestepped controversy by praising cooperation with the U.S. in ending the decades-long conflict in his country.
Mom warns parents after daughter chokes on fidget spinner
Britton was taken by ambulance to her local children's hospital where an X-ray showed the spinner bushing lodged in her esophagus. They're the flavor of the week, but " fidget spinners " may have spun out of control after a Texas girl swallowed part of hers.
"This is a truth hunt", said Democratic Senator Amy Klobuchar.
The airstrikes, in the southern town of Tanf, mark the first time that the USA military deliberately hit the regime out of a perceived threat for American troops, which have steadily increased in numbers in recent months throughout Syria.
In his earlier twitter posts, Trump decried the naming of Robert Mueller, a respected former Federal Bureau of Investigation director, as a special counsel by Deputy Attorney General Rod Rosenstein, an official he himself appointed. Trump himself said he had "an absolute right" as president to share "facts pertaining to terrorism" and airline safety with Russian Federation. Cummings said "we have been waiting for months for the chairman to pick up his so-called subpoena pen".
The focus on leaks has also been embraced by Republicans in Congress, who have urged reporters to pay more attention to the source of their stories - a familiar strategy to deflect the conversation away from bad news. Ryan stuck to that line and told reporters on Wednesday he still has confidence in Trump.
The person who described the Comey memo to the AP was not authorised to discuss it by name and spoke on condition of anonymity.
Nonetheless, if the White House and GOP lawmakers can't agree on ways to offset rate cuts for individuals and companies so a tax package doesn't add to the deficit, they'll either have to settle for temporary changes, or try to get bipartisan support. "I'm not going to get any further comment on that".
Asked Thursday how close he is to making an announcement, Trump answered "soon".