Editor’s Note: Michael D’Antonio is the author of the book “Never Enough: Donald Trump and the Pursuit of Success” and co-author with Peter Eisner of “The Shadow President: The Truth About Mike Pence.” The opinions expressed in this commentary are those of the author. View more opinion articles on CNN.

CNN  — 

It’s a scene that’s often depicted in Hollywood films: The bully picks on a smaller target and manages to paralyze everyone with fear. Then one day, a punch from an unexpected character draws blood. The bully’s vulnerability becomes apparent and suddenly all those who trembled join to fight their former tormentor. Feared but not loved, the bully is vanquished.

Michael D'Antonio

In politics, as in Hollywood, those who’d rather pick a fight than compromise – or, in Donald Trump’s case, act with basic decency – create the conditions for their own downfall. After Speaker of the House Nancy Pelosi’s announcement of a formal impeachment inquiry, there were early signs of the President’s weakness. While the knockout punch has not been delivered, Republicans who were previously staunch allies began to waver.

On Friday, former Sen. Jeff Flake told NPR that at least 35 GOP Senators would support impeaching Trump if they were allowed to vote in secret. “Anybody who has sat through two years, as I have, of Republican luncheons realizes that there’s not a lot of love for the President. There’s a lot of fear of what it means to go against the President, but most Republican senators would not like to be dealing with this for another year or another five years,” he said. Added to Democratic votes, Flake’s estimate of 35 Republicans would make for the two-thirds majority required to remove Trump from office.

As Flake suggests, Republican officials may fear Trump but they do not like him. Consider the President’s penchant for insults and demeaning nicknames and it’s easy to agree with Flake’s logic. Remember that then-candidate Trump mocked and disparaged Sens. Marco Rubio and Ted Cruz as “Little Marco” and “Lyin’ Ted” and you’ll understand why they might have little sympathy for him now.

Trump’s vulnerability was in clear view when Senate Majority Leader Mitch McConnell allowed the upper chamber to vote on a resolution urging the Trump administration to turn over the whistleblower complaint to Congress. The resolution passed unanimously in the GOP-controlled Senate.

The Senate is where the President will make his last stand if he’s subjected to an impeachment trial. Under normal circumstances, a President could expect his party to stick by him, but Trump has acted so outside the norms of the executive office that there’s no guarantee.

A few Republicans already broke with the President since Pelosi’s announcement. Sen. Mitt Romney was the first to say he was troubled by the Ukraine controversy. Sen. Ben Sasse of Nebraska noted there were “obviously some very troubling things” in the rough transcript of a call, which revealed Trump asked Ukraine’s president to investigate his Democratic rival Joe Biden. After the White House released the rough transcript, Sen. Pat Toomey of Pennsylvania said it was “inappropriate.”

Romney, it should be recalled, was subjected to an embarrassing pantomime of an interview for the secretary of state before Trump selected Rex Tillerson over him. Sasse, who will seek re-election in 2020, quietly accepted Trump’s recent endorsement earlier this month. In light of the President’s woes, Sasse seems unconcerned now about courting his wrath. These murmurs of dissent reflect an important shift among Republicans who heretofore quaked at the prospect of a blast from Trump’s Twitter fingers or the humiliation of a sarcastic nickname.

The aggressive style that Trump has brought to national politics is consistent with the man he has always been. During his days as a real estate developer, and later as a media star, he provoked fights with everyone from former New York Mayor Ed Koch to comedian Rosie O’Donnell, never hesitating to insult an opponent’s physical appearance, intelligence, or competence. It was in this time that he began explaining his aggression by saying that he responded when attacked – and felt justified hitting back much harder.

Once he jumped into the 2016 race for president, the hit-harder argument became such a trademark for Trump that even his wife Melania would repeat it in her speeches. “As you may know by now,” she said in April 2016, “when you attack him, he will punch back 10 times harder. No matter who you are, a man or a woman, he treats everyone equal.”

Some people might think a 10-times-harder policy is intentionally threatening and disproportional. And of course, the President, who is notoriously thin-skinned and quick to take offense, often interprets fair criticism, petty snipes, and serious challenges as attacks that warrant public responses.

Combine his endless appetite for fighting – “I like fights, all kinds of fights” he told me in 2014 – and the victim’s mentality he holds, and you get a man who finds himself in constant conflict. You also get a man who craves loyalty but inspires only fear and resentment.

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    The President achieved his dominance over the GOP by making just about everyone in the party afraid of him. This will work for as long as they believe he is truly powerful. Now that the cracks are beginning to show, he cannot count on anyone’s genuine affection or loyalty. And he has given those who will control his fate reason to regard him as expendable.