Sen. Rand Paul, R-Ky., argued Thursday that senior Obama administration officials might be guilty of trying to keep President Trump from getting elected last November.

"Time to investigate high ranking Obama government officials who might have colluded to prevent the election of @realDonaldTrump! This could be WORSE than Watergate!" Paul tweeted Thursday morning.

Paul didn't specify the reason for his tweet, but he wrote it soon after two senior FBI officials involved in the Russian probe were outed for sending text messages that contained anti-Trump sentiments. Republicans have said those texts cast doubt on the conventional wisdom that special counsel Robert Mueller and his team are beyond reproach as they investigate Russia and its possible collusion with then-candidate Donald Trump to help him win the White House.

Mueller's probe has been a constant frustration for Trump as it examines possible collusion, but Trump in recent days has reportedly said he's optimistic that it will end soon without finding any evidence of collusion.

In the meantime, Republicans have been demanding more answers about how the FBI investigated Hillary Clintons' use of a private email server, and Deputy FBI Director Andrew McCabe was expected to testify privately with two House committees on Thursday.