Mr Trump, who became the third president to be impeached in US history on Wednesday, has accused Democrats of “violating the Constitution” with the move, which could delay a trial in the Republican-controlled chamber.
The decision to withhold the articles is believed to be an attempt by Ms Pelosi, the House speaker, to gain leverage as Senate leaders negotiate the rules of the upcoming trial, with Democrats seeking new witnesses and testimony.
“Crazy Nancy, she’s crazy,” Mr Trump told the conference, organised by the conservative student group Turning Point USA, before branding the impeachment process as “so unfair”.
The president has been impeached on two articles - abuse of power and obstruction of Congress - over allegations that he withheld US military aid and a White House visit to Ukraine to force its leader into announcing an investigation into his 2020 election rival Joe Biden.
Mr Trump has denied any wrongdoing, even as a number of high-profile US diplomats and foreign service officials have testified about their concerns over his conduct.
However, impeachment was not the only thing on the president's mind as he began his speech by repeating one of his strangest lies about a supposed “war on Christmas”.
“You remember they were trying to take Christmas out of Christmas? They didn’t want to let you say ‘Merry Christmas,’” he told the crowd of young supporters.
“You’d go around, you’d see department stores they’d have everything red, snow, beautiful, ribbons, bows. Everything was there but they wouldn’t say ‘Merry Christmas’. They’re all saying ‘Merry Christmas’ again.
"That's the least I could do."
In 2016, Mr Trump claimed Americans would be able to say “Merry Christmas in every store” during his presidency, suggesting falsely that the phrase was not used anymore.
Despite his impeachment in the House of Representatives, the president is expected to be acquitted of both charges in the Senate.
On Saturday, Mr Trump lashed out at Democratic members of Congress who backed impeachment, accusing them of not believing in democracy and trying to "overthrow" the 2016 election result.
“The Democrat Party is trying to shred our Constitution, tear down our history and erase the nation's borders,” Mr Trump said.
“Each of you are on the front lines of defending our way of life. The radical left doesn't stand a chance against young conservatives who put America first,” he told the student crowd.
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