President Trump argued Thursday that his political opponents are jumping from one fake allegation to the next in order to try to bring down his presidency.

"They made up a phony collusion with the Russians story, found zero proof, so now they go for obstruction of justice on the phony story. Nice," Trump wrote on Twitter.

The Washington Post reported Wednesday that former FBI Director Robert Mueller, who is overseeing the Russia probe, is now investigating whether the president attempted to obstruct justice in the investigation.

Former FBI Director James Comey told the Senate Intelligence Committee last week the president was originally not under investigation, but Trump is reportedly now part of the probe.

Officials say that despite Comey's reassurances Trump wasn't under investigation, that changed after he was fired last month.

The investigation into whether Trump obstructed justice reportedly began days after Comey's firing on May 9.

The White House is referring questions about the Russian probe to Marc Kasowitz, Trump's personal lawyer.

"The FBI leak of information regarding the president is outrageous, inexcusable and illegal," Mark Corallo, a spokesman for Kasowitz, told the Washington Post.

The bureau is also looking into allegations of collusion between the Trump campaign and Russian officials, though there so far hasn't been any evidence to support that claim.

The Russia investigation also involves whether any financial crimes were committed by Trump associates.

According to officials who spoke to the Washington Post, Director of National Intelligence Dan Coats, National Security Agency Director Mike Rogers and his former deputy Richard Ledgett will speak with Mueller's investigators. Those interviews could come as early as this week.

Coats and Rogers testified before the Senate Select Committee on Intelligence last week and were asked repeatedly about their private conversations with Trump. But neither Coats nor Rogers shared the details of those discussions.

It was reported, though, that Trump had asked the two intelligence officials to publicly deny the existence of evidence showing collusion between his campaign and the Kremlin.

Coats told associates that on a separate occasion, Trump asked whether he could intervene with Comey to push him to ease off the FBI's investigation into former National Security Adviser Michael Flynn.