(CNN) A Democratic senator is sending a letter to the Justice Department, asking whether Attorney General Jeff Sessions violated his recusal from investigations into the 2016 presidential election when he recommended the firing of former FBI Director James Comey.

Sen. Chris Coons, who sits on the Senate judiciary committee, will send the letter Thursday to the Justice Department's Office of Professional Responsibility, requesting more information about the scope of Sessions' pledges of recusal.

The letter comes as Washington buzzes with speculation about Sessions' fate following ramped-up attacks from President Donald Trump, who's criticized his own attorney general in scathing tweets and public interviews.

Coons' letter, along with comments from Trump, illustrates the pressure that Sessions is facing from opposing sides -- from Democrats who felt he was not strong enough in his recusal, to the President, who felt he should not have recused himself at all.

Sessions, during a January confirmation hearing, offered to recuse himself from any investigations involving the Hillary Clinton email scandal.

In March, as questions emerged about Sessions' past contact with a now former Russian ambassador, Sessions formally recused himself in "matters that deal with the Trump campaign."

Comey's firing in May, which came at the recommendation of Sessions, was initially attributed to Comey's handling of the Clinton email investigation last year. Trump later stated that he was already planning to fire Comey and expressed frustration that he was still being tied to the Russia investigation.

With a deadline of August 10, Coons' letter asks for communications within the DOJ or the White House involving Sessions' recusal as well as any documentation on procedures to ensure compliance of his recusal. Among other things, the letter also asks for standards and procedures for when a recusal is violated.

"Whether Mr. Comey was fired because of the Clinton email investigation or the investigation of collusion between the Trump campaign and Russia during the presidential election, the reason for Mr. Comey's dismissal falls squarely within Attorney General Sessions' recusals," Coons writes in the letter.

House Democrats issued a similar letter to the Justice Department's inspector general in June, and multiple senators asked Sessions about his recusal and the Comey firing when he testified before the Senate Intelligence Committee last month.

In that hearing, Sessions reiterated his recusal from the Russia inquiry.

"I have no knowledge about this investigation as it is ongoing today beyond what has been reported," he said. "I don't even read that carefully. I have taken no action whatsoever with regard to any such investigation."

As for the firing of Comey, Sessions said that he made the recommendation based on concerns about Comey's leadership, as well as concerns outlined in a memo by Deputy Attorney General Rod Rosenstein, who detailed apprehension about Comey's handling of the Clinton email scandal.

"It is absurd, frankly, to suggest that a recusal from a single specific investigation would render the attorney general unable to manage the leadership of the various Department of Justice law enforcement components that conduct thousands of investigations," Sessions said.

While the attorney general addressed his recusal from the Russia probe repeatedly in the June hearing, Democrats like Coons are trying to draw more attention to Sessions' earlier pledge, before he was confirmed, to recuse himself from Clinton-related investigations as well.

In his January confirmation hearing, Sessions pledged to recuse himself "from any questions involving those kind of investigations that involve Secretary Clinton and that were raised during the campaign or to be otherwise connected to it."