WASHINGTON (AP) — On the eve of almost-certain impeachment, President Donald Trump fired off a furious letter Tuesday to House Speaker Nancy Pelosi denouncing the “vicious crusade” against him, while Democrats amassed the votes they needed and Republicans looked ahead, vowing to defend Trump at next month’s Senate trial.

Trump, who would be  just the third U.S. president to be impeached, acknowledged he was powerless to stop Wednesday’s vote. He appeared to intend his lengthy, accusatory message less for Pelosi than for the broad audience of citizens watching history unfolding on Capitol Hill.

He accused the Democrats of acting out of “Trump Derangement Syndrome,” still smarting from their 2016 election losses. “You are the ones bringing pain and suffering to our Republic for your own selfish, personal political and partisan gain.” 

Portraying himself as a blameless victim, as he often does, Trump compared the impeachment inquiry to the “Salem Witch Trials.” Asked later if he bore any responsibility for the proceedings, he said, “No, I don’t think any. Zero, to put it mildly.”

Pelosi, who warned earlier this year against pursuing a strictly partisan impeachment, nonetheless has the numbers to approve it. According to a tally compiled by The Associated Press, Trump is on track to be formally charged by a House majority on Wednesday. Lawmakers were scheduled to convene this morning with final votes anticipated by early evening.

“Very sadly, the facts have made clear that the President abused his power for his own personal, political benefit and that he obstructed Congress,” Pelosi wrote to colleagues. “In America, no one is above the law.”

“During this very prayerful moment in our nation’s history, we must honor our oath to support and defend our Constitution from all enemies, foreign and domestic,” she said.

No Republicans have indicated they will support the the two articles of impeachment, for abuse of power and obstruction of Congress, setting up a close-to-party-line vote. 

One by one, centrist Democratic lawmakers, including many first-term freshmen who built the House majority and could risk their reelection in districts where the president is popular, announced they would vote to impeach. 

Rep. Abby Finkenauer, D-Iowa, referred to the oath she took in January as she was sworn into office as guiding her decision. She announced support for both articles of impeachment to “honor my duty to defend our Constitution and democracy from abuse of power at the highest levels.”

Republicans disagreed, firmly.

Senate Majority Leader Mitch McConnell set the partisan tone for the next step, as attention will shift to the Senate which, under the Constitution, is required to hold a trial on the charges. That trial is expected to begin in January. 

“I’m not an impartial juror,” McConnell declared. The Republican-majority chamber is all but sure to acquit the president.

From Alaska to Florida, tens of thousands of Americans marched in support of impeachment Tuesday evening, from a demonstration through a rainy Times Square to handfuls of activists standing vigil in small towns. They carried signs saying “Save the Constitution – Impeach!!!!” and “Criminal-in-Chief.”

 “I really believe that the Constitution is under assault,” said one protester, 62-year-old Glenn Conway, of Holly Springs, North Carolina, attending his first political rally in 30 years. “I think we have a president at this point who believes he’s above the law.”

Trump is accused of abusing his presidential power in a July phone call in which he asked the newly elected president of Ukraine, a U.S. ally facing an aggressive Russia at its border, to “do us a favor” by investigating Democrats, including his potential 2020 rival Joe Biden. At the time, President Volodymyr Zelenskiy was hoping for a coveted White House meeting that would bolster his standing with Ukraine’s most important ally. He also was counting on nearly $400 million in military aid Congress had approved to counter Russia. The White House had put the money on hold — as leverage, the Democrats say.

In his letter on Tuesday, Trump defended his “absolutely perfect” phone call that sparked the impeachment inquiry. He also tried to justify anew the Ukrainian investigations he wanted into Biden. And he disputed the charges of abuse of power and obstruction of Congress’ investigation.

Conceding the House vote, he said he wanted to set his words down “for the purpose of history.”

Asked on CNN about Trump’s lengthy complaints about his treatment, Democratic Rep. Eric Swalwell of California dismissed what he called a “childish, whiny letter.”

House Democrats continued to march toward Wednesday’s debate and votes.

“It’s unfortunate that we have to be here today, but the actions of the president of the United States make that necessary,” said Chairman Jim McGovern, D-Mass., gaveling the Rules Committee, which met through the day, with lawmakers arguing over the parameters for the debate. 

McGovern said, “Every day we let President Trump act like the law doesn’t apply to him, we move a little closer” to rule by dictators.

The top committee Republican, Tom Cole of Oklahoma, said, “When half of Americans are telling you what you are doing is wrong, you should listen.”

Lawmakers crossing party lines face consequences. One freshman Democrat, Jeff Van Drew of New Jersey, is indicating he will switch parties to become a Republican after opposing impeachment. Earlier this year, Michigan conservative Rep. Justin Amash left the GOP when he favored impeachment. 

One new Democratic congressman, Jared Golden of Maine, said he would vote to impeach on abuse of power but not obstruction.

Hoping to dispatch with lengthy Senate proceedings, McConnell rejected Senate Democrats’ push for fresh impeachment testimony and made a last-ditch plea that House Democrats “turn back from the cliff” of Wednesday’s expected vote.

“Impeachment is a political decision,” McConnell said. “The House made a partisan political decision to impeach. I would anticipate we will have a largely partisan outcome in the Senate. I’m not impartial about this at all.’’ 

McConnell’s remarks Tuesday effectively slapped the door shut on negotiations for a deal proposed by the Democratic leader, Sen. Chuck Schumer, who wants to call top White House officials for the Senate trial.

Schumer’s proposal was the first overture in what were expected to be negotiations between the two leaders. Trump wants a relatively broad, perhaps showy, Senate proceeding to not only acquit but also vindicate him of the impeachment charges. 

McConnell and most other GOP senators prefer a swift trial to move on from impeachment. Many centrist House Democrats also are ready to vote and move on. Still, Schumer wants to hear from John Bolton, Mick Mulvaney and other current and former Trump officials who were instructed by the president not to appear in the House proceedings.

“Why is the leader, why is the president so afraid to have these witnesses come testify?” asked Schumer from the Senate floor. “They certainly ought to be heard.”

Trump “betrayed the Nation by abusing his high office to enlist a foreign power in corrupting democratic elections,” the impeachment resolution says. “President Trump, by such conduct, has demonstrated that he will remain a threat to national security and the Constitution if allowed to remain in office.” 

Trump has promoted lawyer Rudy Giuliani’s investigation of Biden and a widely debunked theory that it was actually Ukraine, not Russia, that interfered in the 2016 election, a  conspiracy-laden idea  that most other Republicans have actively avoided.

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Associated Press writers Laurie Kellman, Matthew Daly, Alan Fram and Darlene Superville in Washington, David Eggert in Rochester, Mich., Gary Robertson in Raleigh, N.C., and Steve Karnowski in Minnesota contributed to this report.