FILE - Sen. Richard Blumenthal, D-Conn., and other Democrats respond to questions from reporters about President Donald Trump reportedly sharing classified information with two Russian diplomats during a meeting in the Oval Office on Capitol Hill in
FILE - Sen. Richard Blumenthal, D-Conn., and other Democrats respond to questions from reporters about President Donald Trump reportedly sharing classified information with two Russian diplomats during a meeting in the Oval Office on Capitol Hill in

CAPITOL HILL - President Donald Trump's criticism of a stepped-up Russia probe as a "witch hunt" prompted a sharp reaction from Democrats on Capitol Hill.

The president took to Twitter to disparage the appointment of a special counsel with enhanced powers to investigate Russia's meddling in last year's presidential election and any collusion by the Trump campaign, writing, "This is the single greatest witch hunt of a politician in American history!"

The comment did not sit well with Democratic Senator Richard Blumenthal.

"President Trump again is demonstrating his contempt for the rule of law," he said.

FILE - FBI Director Robert Mueller listens as he t
FILE - FBI Director Robert Mueller listens as he testifies on Capitol Hill in Washington, June 13, 2013.

Regarding the naming of Robert Mueller as a special counsel to lead the investigation, Blumenthal said Mueller "has not only the expertise and experience, he has the grit and backbone to stand up to potential political influence. And the best sign that he will need that grit is Donald Trump's tweet about [a] witch hunt."

Some Republicans continue to question the need for an independent prosecutor, noting that multiple probes have been under way for months. But Senator John Cornyn of Texas said Mueller is perhaps the single most-qualified person to get the facts for the American people.

"We could use some conclusions based on facts here in Washington with the relentless torrent of rumor, gossip and suspicion, but very few facts," Cornyn said.

The entire Senate is preparing to be briefed behind closed doors by the man who appointed Mueller, Deputy Attorney General Rod Rosenstein. 

WATCH: What is a special counsel?