Sen. Chuck Grassley Charles (Chuck) Ernest GrassleyGardner signals support for taking up Supreme Court nominee this year Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee McConnell digs in on vow to fill Ginsburg's Supreme Court seat MORE (R-Iowa) sent a warning shot to the White House on Wednesday night, saying he wouldn't take up the nomination of any potential successor to Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE this year.

"Everybody in D.C. [should be] warned that the agenda for the Judiciary Committee is set for rest of 2017. Judges first subcabinet 2nd / AG no way," Grassley said in a tweet on Wednesday evening.

Everybody in D.C. Shld b warned that the agenda for the judiciary Comm is set for rest of 2017. Judges first subcabinet 2nd / AG no way — ChuckGrassley (@ChuckGrassley) July 27, 2017

Grassley is the chairman of the Judiciary Committee and served with Sessions on the panel. He could effectively block any attorney general nominee from getting a hearing or a vote if Sessions were to be fired or step down — which he has not said he would do.

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His comments come as Trump has intensified his public criticism of Sessions, a former senator and his first supporter in the upper chamber.

In the most recent morning tweet storm venting his frustration with the attorney general, he questioned why Sessions hasn't replaced acting FBI Director Andrew McCabe.

Why didn't A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got.... — Donald J. Trump (@realDonaldTrump) July 26, 2017

Trump has also privately discussed using a recess appointment to try to name Sessions's successor without having to get congressional approval, according to The Washington Post. A White House official told the Post that action isn't "imminent."

Congressional Democrats have pledged they will block such a move by forcing the Senate to hold pro-forma sessions, which would stymie any attempts by Trump to make a recess appointment.

Senate Republicans, who have a large amount of respect for Sessions, have publicly backed their former colleague in his ongoing feud with Trump and publicly downplayed the chances that the president fires him.

Sen. John Cornyn John CornynTumultuous court battle upends fight for Senate Texas Democrats roll out first wave of planned digital ads as Election Day nears Calls grow for Biden to expand election map in final sprint MORE (Texas), the No. 2 Senate Republican, said earlier Wednesday that Trump and Sessions needed to "sit down and work it out."

"Well, it's the president's prerogative, but he's then going to jeopardize, potentially, his ability to get anything else done here. And I don't think that should be his desire or productive," Cornyn added to NBC News.