Washington (CNN) With his impeachment now all-but-certain , President Donald Trump and his allies are beginning to look past the House of Representatives, shifting their sights to the Republican-led Senate where the President will face trial.

Trump, who as recently as Wednesday lamented impeachment as a "dirty word," has struggled to accept the prospect of becoming the third President in history to be impeached . But the President and White House officials are now signaling they will mount a robust defense in the Senate and look to turn the tables on Democrats during the President's trial -- including by digging in on the President's unsubstantiated claims of corruption leveled at former Vice President Joe Biden.

Trump's new reality began to set in as he returned from the NATO summit in London , where he canceled a scheduled news conference after a video surfaced appearing to show several world leaders, including Canadian Prime Minister Justin Trudeau, mocking Trump's impromptu question-and-answer sessions with reporters alongside foreign counterparts.

Trump was "annoyed" and "bothered" by the hot mic video and people close to him said he fumed about Trudeau as he prepared to leave London.

But his attention quickly turned to the unfolding impeachment hearing after he boarded Air Force One to return to Washington. On the flight home, with the TVs tuned to the hearing, the President praised the Republican questioning of the constitutional scholars who testified on Wednesday and coordinated the White House's forceful response to one of the witnesses invoking his 13-year-old son's name

For months, Trump has partly invited but largely dreaded the prospect of being only the third President in history to be impeached. But with House Democrats now crystallizing their intentions, the President and his White House are steeling themselves for what comes next.

"If you are going to impeach me, do it now, fast, so we can have a fair trial in the Senate, and so that our Country can get back to business," Trump tweeted Thursday morning as he awaited Pelosi's remarks. "We will have Schiff, the Bidens, Pelosi and many more testify, and will reveal, for the first time, how corrupt our system really is."

After House Speaker Nancy Pelosi accused Trump of having "abused his power for his own personal political benefit" and declared that the House Judiciary Committee will "proceed with articles of impeachment," the President hinted at the Republican wall Democrats are likely to run up against in the Senate.

"The good thing is that the Republicans have NEVER been more united," Trump tweeted. "We will win!"

Trump and his allies were also quick to signal that they view the trial in the Republican-controlled Senate as an opportunity to score political points and deflect from the central allegations Trump is facing. Just as Trump pointed to a wish-list of Democrats he would see questioned during a Senate trial, his campaign manager relished the prospect of a "fair trial in the Senate" and the opportunity to "expose the Swamp for what it is."

At the White House, officials touted the first impeachment hearing in the House Judiciary Committee as a good day for the President and argued that it was the culmination of weeks of hearings that have failed to swing the public in favor of impeachment.

"The public hasn't been moved by any of this. It strikes along partisan lines like you'd expect," one White House official said.

While more Americans now support impeaching and removing Trump from office than those who do not, Democrats have struggled to sway independents and voters in key battleground states.

With that in mind, White House lawyers have spent the last several weeks almost singularly focused on building out the President's legal defense in preparation for a Senate trial, sources familiar with the matter said.

There are two aspects the White House is focused on as it prepares for the potential Senate trial -- the communications strategy and the legal strategy. An administration official says Pat Cipollone will take the lead as the main lawyer in the potential senate trial supported by his deputies, including Mike Purpura and Pat Philbin. The officials say Cipollone "built his team with many trial lawyers precisely for this eventuality."

Cipollone is also engaging regularly with lawmakers, including Senate Majority Leader Mitch McConnell. And White House advisers Tony Sayegh and Pam Bondi are meeting regularly with lawmakers and their staff on Capitol Hill to coordinate on messaging.

The White House has previously urged Republican senators to not drag it out.

And White House officials say the burden is on the Democrats to prove Trump did something wrong, not for the White House to prove he did something right, and officials believe the Democrats have not succeeded in that regard to dramatically sway public opinion.

The President "wants his case fully made in the Senate," White House legislative affairs director Eric Ueland told reporters on Wednesday. "We need witnesses as part of our trial and a full defense of the President on the facts."