President Trump on Monday blasted congressional Democrats for “zero fairness” in their bid to impeach him just one day before the Senate trial officially begins.

“They didn’t want John Bolton and others in the House. They were in too much of a rush. Now they want them all in the Senate. Not supposed to be that way!” Trump tweeted Monday, referring to Democrat-sought witnesses like Bolton, his ex-national security adviser.

“Cryin’ Chuck Schumer is now asking for ‘fairness,’ when he and the Democrat House members worked together to make sure I got ZERO fairness in the House,” he continued. “So, what else is new?”

The president’s tweet comes just hours after Senate Democratic Leader Chuck Schumer, D-N.Y., vowed to “force votes on witnesses and documents” in the impeachment trial, which is slated to begin Tuesday.

“We Democrats aim to get the truth,” Schumer said. “Make no mistake about it, we will force votes on witnesses and documents, and it will be up to four Republicans to side with the Constitution, to side with our democracy, to side with the rule of law, and not side, in blind obeisance, to President Trump and his desire to suppress the truth. Because, in my judgment, he probably thinks he’s guilty.”

DEMOCRATS CLASH WITH GOP OVER PROSPECT OF CALLING HUNTER BIDEN IN IMPEACHMENT TRIAL

The topic of witnesses has been at issue since the House passed the articles of impeachment—charges of abuse of power and obstruction of Congress-- in mid-December. House Speaker Nancy Pelosi, D-Calif., had been holding onto the articles in a bid to extract favorable terms for the trial, including a commitment from Senate Majority Leader Mitch McConnell, R-Ky., to call witnesses, but she ended her delay last week after he made it clear he was not willing to negotiate.

McConnell has repeatedly said that the resolution to govern the impeachment trial in the Senate would mirror the one used for then-President Bill Clinton’s impeachment trial in 1999. That resolution will set a time frame for the trial to begin, with the opportunity for lawmakers to determine how to proceed on potential witness testimony and additional documents later, after both the president’s defense and the prosecution make their opening statements.

Schumer, though, suggested McConnell was “being so secretive about his proposal” to call witnesses, and that Trump was “afraid of the truth.”

As for possible witnesses, Democrats have called for testimony from Bolton for weeks. Bolton, earlier this month, signaled that he would be open to testifying, and would comply with the request, should he receive a congressional subpoena.

Republicans, though, have warned of “witness reciprocity,” which would mean that GOP senators could request testimony from their own witnesses in exchange for Democrat-sought witness testimony.

Republicans have not committed to doing so, but many have floated calling former Vice President Joe Biden’s son, Hunter, as a witness.

Hunter emerged as a central figure in the Ukraine controversy due to his business dealings.

SCHUMER: DEMS WILL 'FORCE VOTES ON WITNESSES AND DOCUMENTS' IN TRUMP IMPEACHMENT TRIAL

The inquiry began when a whistleblower reported that Trump had pushed Ukrainian President Volodymyr Zelensky to launch an investigation into the Biden family’s dealings in Ukraine—specifically, why Joe Biden pressured former Ukrainian President Petro Poroshenko to fire a top prosecutor, Viktor Shokin, who was investigating Ukrainian natural gas firm Burisma Holdings, where Hunter held a lucrative role on the board, bringing in a reported $50,000 per month.

House Republicans noted that in testimony from former State Department official George Kent, he raised concerns about "the appearance of a conflict of interest stemming from Mr. Biden's position on Burisma's board."

At the time, the former vice president was running U.S.-Ukraine policy under former President Barack Obama.

Fox News' Vandana Rambaran contributed to this report.