Donald Trump is feeling pressed—and understandably so.

The president has penned an angry six-page letter to Speaker Nancy Pelosi (D-Calif.), accusing her and House Democrats of "subverting America's democracy" by pursuing impeachment. The letter was sent Tuesday, a day before the House is expected to vote on two charges against Trump, who is accused of extorting a foreign power to investigate a political rival. According to the Associated Press, the majority of the House is in favor of impeachment, setting the stage for Trump becoming the third U.S. president to ever be impeached. 

"This impeachment represents an unprecedented and unconstitutional abuse of power by Democrat Lawmakers, unequaled in nearly two and a half centuries of American legislative history," Trump wrote in the letter, before reiterating his claims of innocence. "... You have cheapened the importance of the very ugly word, impeachment! By proceeding with your invalid impeachment, you are violating your oaths of office, you are breaking allegiance to the Constitution, and you are declaring open war on American Democracy."

The charges against Trump stem from his July phone call with Ukrainian President Volodymyr Zelensky, whom he urged to investigate Democratic presidential candidate Joe Biden and his son, Hunter Biden. Trump froze nearly $400 million in military aid for Ukraine shortly the phone call took place—a detail that sparked allegations of a quid-pro-quo offering. The first article of impeachment charges Trump with abuse of power, while the second charges him with obstruction of Congress; the latter is based on his refusal to comply with documents requests during the impeachment inquiry, as well as blocking certain testimony. Trump has denied any wrongdoing, and told Pelosi that she and the Democrats would be on the wrong side of history if they did not halt the impeachment proceedings.

"It is time for you and the highly partisan Democrats in Congress to immediately cease this impeachment fantasy and get back to work for the American People. While I have no expectation that you will do so, I write this letter to you for the purpose of history and to put my thoughts on a permanent and indelible record," he wrote. "...You are the ones interfering in America’s election. You are the ones subverting America’s Democracy. You are the ones Obstructing Justice ... I have no doubt the American people will hold you and the Democrats fully responsible in the upcoming 2020 election. They will not soon forgive your perversion of justice and abuse of power."

You can read his full letter and reactions to the missive below.

If the House approves the articles of impeachment, as expected, the matter will then go to the Republican-controlled Senate, where it will likely end in an acquittal.