• House Speaker Nancy Pelosi is making President Donald Trump squirm.
• Pelosi's refusal to transmit the articles of impeachment against Trump to the Senate has robbed the president of what he wants most: "total and complete exoneration" following a trial.
• Asked about Trump's mind-set in recent days, one Republican strategist in frequent contact with the White House told Insider Trump was incensed about impeachment because he believes it undermines his political prowess.
• The strategist said Trump was angry because the allegations against him suggest "that he needs outside help to win an election, that he can't do it on his own. And he thinks that's bulls---."
• A person who was close to Trump's legal team during the Russia probe also told Insider the cascade of witness testimony, more than anything else, grated on the president's nerves.
• "For a man who puts personal loyalty above everything else, this was something he never saw coming," the person said. "He couldn't stop them, so he decided to smear them, but at the end of the day, all he could do is sit back and watch it happen."
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House Speaker Nancy Pelosi is doing to President Donald Trump what no one else has in the nearly three years since he took office: She's making him squirm.

In the wake of an impeachment inquiry and with a looming trial in the Senate, the president has become increasingly frustrated by Pelosi's unprecedented decision to withhold the two articles of impeachment against him from the upper chamber until Majority Leader Mitch McConnell guarantees a fair and impartial trial.

Pelosi's refusal to transmit the articles of impeachment to the Senate has robbed the president of what he wants most: "total and complete exoneration" following a trial.

Trump, for his part, has made no secret of his fury. He spent Christmas evening ranting about Pelosi and impeachment to his 68 million Twitter followers.

"Why should Crazy Nancy Pelosi, just because she has a slight majority in the House, be allowed to Impeach the President of the United States? Got ZERO Republican votes, there was no crime, the call with Ukraine was perfect, with 'no pressure,'" Trump tweeted on Wednesday night.

He added, "She said it must be 'bipartisan & overwhelming,' but this Scam Impeachment was neither. Also, very unfair with no Due Process, proper representation, or witnesses. Now Pelosi is demanding everything the Republicans weren't allowed to have in the House. Dems want to run majority Republican Senate. Hypocrites!"

This week's complaints were just the latest in Trump's monthslong Twitter tear against Pelosi and the impeachment inquiry.

The day after House Democrats unveiled two articles of impeachment this month — one charged the president with abuse of power, and the other charged him with obstruction of Congress — Trump posted 60 tweets and retweets before noon.

The public airing of grievances is a staple of the Trump presidency.

In the three years he's been in office — and long before that — Trump has made a habit of using Twitter and the media to lob attacks at everyone and everything, including Democrats, the former special counsel Robert Mueller, former Secretary of State Hillary Clinton, former California Gov. Arnold Schwarzenegger, the actress Rosie O'Donnell, and the mainstream media.

Trump has also had legal troubles before.

This month, Trump paid $2 million to eight charities after a New York judge ruled that he and his family had used the now defunct Trump Foundation as a slush fund to bolster his campaign and pay off business expenses.

Last year, Trump agreed to a $25 million settlement to be paid to former students of Trump University, which then-New York Attorney General Eric Schneiderman described as a "sham university" that swindled "thousands of Americans out of millions of dollars."

'One way or another, everything goes back to 2016'

But impeachment has struck a particularly sensitive nerve with the president.

Asked about Trump's mind-set in recent days, one Republican strategist in frequent contact with the White House, who requested anonymity to discuss internal conversations, told Insider Trump was incensed about impeachment because he believes it undermines his political prowess.

"One way or another, everything goes back to 2016," the strategist said. "For two years after he took office, the president had the Russia cloud hanging over him."

"To him, that investigation was synonymous with the belief that he didn't win the White House on his own, that he had help from the Russians," the strategist added. "Looking ahead with the 2020 election, he's facing new allegations once again that he needs outside help to win an election, that he can't do it on his own. And he thinks that's bulls---."

Exacerbating things further is Pelosi's position as the tip of the Democratic spear.

The House speaker has been a thorn in the president's side since January, after the Democratic Party resumed control of the House of Representatives.

In the months since, Trump has been forced to make concession after concession to Pelosi and the Democrats — a major adjustment for a president who sees himself as having the "absolute" right to govern as he sees fit and whose power went virtually unchecked while Republicans controlled both chambers of Congress.

'As long as those articles of impeachment sit in Nancy Pelosi's hands, Trump is powerless'

The president got his first taste of Pelosi's strategy in January, in the middle of a government shutdown, as the White House and congressional Democrats fought over Trump's demand that the federal budget include billions in funding for a border wall.

In the middle of that fight, Trump sent a letter to the House speaker canceling a trip she was scheduled to take to Afghanistan on a government-funded military plane.

In response, a few days later, Pelosi disinvited the president from giving the State of the Union before Congress. Eventually, Trump was forced to cave and agreed to reopen the government without the border-wall funding.

To some, Politico Magazine said, it even looked like Pelosi used Trump's State of the Union to project power. At one point in particular during the speech, the Democratic leader smiled and pointed at the president while applauding him.

Politico reported that while some observers viewed the moment as an attempt to smooth out the division between the two sides, others saw it as an indulgent and "exaggerated recognition that a parent might give a toddler in need of positive reinforcement."

Since then, Pelosi has continued her refusal to give an inch to the White House unless Democrats receive something in return.

In September, she exercised the full extent of her power as the leader of the House when she announced an impeachment inquiry into Trump after revelations that he withheld nearly $400 million in military aid to Ukraine while attempting to strong-arm the Ukrainian president into publicly announcing investigations targeting Trump's 2020 rival former Vice President Joe Biden.

Adding fuel to the fire was the fact that Trump was not only unable to stop the investigation but also helpless against the flood of career nonpartisan national-security officials and foreign-service officers who stepped forward to testify against him.

A person who was close to Trump's legal team during the Russia probe told Insider the cascade of witness testimony, more than anything else, grated on the president's nerves.

"He's called them Never Trumpers, but these people worked for him, and some still do," the person said. "For a man who puts personal loyalty above everything else, this was something he never saw coming. He couldn't stop them, so he decided to smear them, but at the end of the day, all he could do is sit back and watch it happen."

The person added: "And as long as those articles of impeachment sit in Nancy Pelosi's hands, Trump is powerless."