Washington (CNN) In some ways he's been expecting it for years. But the imminent prospect of impeachment is still weighing heavily on Donald Trump, who is likely to join the small club of presidents to face a formal impeachment vote as early as next week.

It's not the history-making Trump prefers. While he's been quick to downplay the moment as the culmination of a partisan witch hunt led by angry Democrats, people familiar with his mindset say he's taken a somber view in private as his impeachment looms.

No president wants to be impeached and Trump is no different, despite the political upside his advisers insist will come when voters cast ballots next year. Long strings of early morning tweets and retweets have only amplified the sense that Trump is agitated as the fateful vote nears.

During a campaign rally on Tuesday night, Trump dismissed the impeachment inquiry against him as "flimsy, pathetic, ridiculous," telling the Pennsylvania crowd it was just a bunch of "impeachment crap."

"This is the lightest, weakest impeachment," Trump said. "You know our country's had, actually, many impeachments. You'd call judges and lot of, many impeachments, but it was on today everybody said this is impeachment-lite. This is the lightest impeachment in the history of our country, by far. It's not even like an impeachment."

But while the President is minimizing the articles of impeachment leveled against him , several sources say that privately his stance remains the same.

"I think he's been preparing for this for some time," a Trump adviser said, adding the President has appeared somewhat taken aback that his actions toward Ukraine are ultimately what led to his likely impeachment.

"Frankly, I think he's a little surprised it's the Ukraine thing that's done it," the adviser said.

Trump still views impeachment through a serious lens. He does not want to be part of a notorious group of presidents who have been impeached, a bracket that includes Bill Clinton, whose own impeachment Trump has brought up repeatedly and critically in the past, saying it's what people remember most about Clinton's time in office. Trump has said he does not want his own legacy to face a similar fate.

Clinton himself -- the only living president to have been impeached, though he was acquitted by the Senate -- has publicly counseled Trump to continue going about his job without becoming consumed with the proceedings, as he attempted to do during his own impeachment inquiry. It's advice Trump has ignored.

"Congress is doing what they believe is right," Clinton said while leaving an event in New York City on Tuesday. "The rest of us should go about our lives, and all of us commenting on it won't have anything to do with it. They should do their job, I'll do mine."

Even developments Trump would ordinarily relish have left him with a sour taste. He's suggested that legacy items, such as a renegotiated North American trade agreement , are wrapped up in the impeachment mire.

"Without the impeachment, they would have never approved it, in my opinion," Trump said of the US-Mexico-Canada trade agreement, which Democrats announced Tuesday they were ready to support after extensive negotiations with the administration. Passage of the NAFTA replacement would amount to one of his top legislative achievements.

"The impeachment is the reason they approved it and interestingly one hour after the news conference, they went out and did a news conference on the big trade deal," he said, shrugging as he departed the White House under a black umbrella for his campaign rally.

Trump regularly peppers aides over how impeachment is polling . While some of those aides have tried to argue the potential political benefits of impeachment, Trump has still privately griped about going through it.

And like during other moments of crisis, Trump is fixated on how the news media is portraying him.

"The coverage bugs him," a Trump campaign adviser said.

A president facing impeachment being in a cloudy mood is hardly a revelation. For Trump, the prospect has been looming for nearly as long as he's been president, as Democrats publicly floated the idea -- a fact Trump's allies now argue is evidence of a rigged-from-the-start mindset.

When it became clear a year ago that Democrats were likely to take control of the House of Representatives, the odds for impeachment increased and with them, Trump's worries.

And as the Ukraine scandal rapidly unspooled during Trump's visit to New York in September for the yearly United Nations meetings -- eventually prompting the formal impeachment inquiry -- the President appeared distracted and unfocused during conversations, according to advisers.

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Aides say there's little expectation of a reset once the House holds its impeachment vote, which could occur as soon as next week following a vote in the Judiciary Committee. Senate Majority Leader Mitch McConnell says he won't begin a Senate trial until the new year, despite Trump's publicly stated desire to get the proceedings over with.

The two men are at odds over how the trial might look . In conversations with the White House, the Kentucky Republican has made clear he hopes to end the trial as soon as he can, an effort to both get impeachment off his lap and protect his conference from potentially damaging votes should the process break out into partisan warfare.

But Trump has made clear to his advisers that rather than end the trial quickly, he is hoping for a dramatic event, according to two people familiar with his thinking -- complete with high-profile witnesses testifying live on Capitol Hill.

For now, there is expected to be a public lull over the Christmas holidays between the House vote and -- if he's impeached -- the Senate trial.

In private, however, aides aren't expecting a restful break. Trump is planning to spend more than two weeks at his Florida resort plotting his Senate defense.