• Sean Parnell, the Republican Senate candidate in Pennsylvania endorsed by former President Donald Trump, suspended his campaign Monday after losing custody of his children.
• Parnell's estranged wife accused him of past domestic abuse, and a judge found the allegations to be credible.
• Parnell was a leading GOP candidate in the closely watched race to replace retiring Sen. Pat Toomey, a Republican in a swing state that Democratic President Joe Biden won.

Sean Parnell, the Republican who was endorsed by former President Donald Trump in next year's Pennsylvania U.S. Senate race, suspended his campaign Monday after losing custody of his children in a divorce marked by allegations of past domestic abuse.

Parnell was a leading GOP candidate in the closely watched race to replace retiring Sen. Pat Toomey, a Republican in a swing state that Democratic President Joe Biden won in 2020.

With a 50-50 split in the Senate, the winner of this open seat in 2022 could determine which party controls the Senate. Several top Democrats, including Lt. Gov. John Fetterman and U.S. Rep. Conor Lamb, are also running for the seat.

Trump's endorsement of Parnell's campaign had pushed the former Army Ranger out ahead of other Republican primary candidates, including Trump's former ambassador to Denmark.

But Parnell's campaign has been on the rocks ever since court records surfaced in September of protective orders granted to Parnell's estranged wife, Laurie Snell in 2017 and 2018.

In a ruling Monday, the judge overseeing Parnell's divorce said he believed Snell's allegations that Parnell had choked her and hit their children. The ruling awarded Snell full legal custody of the couple's three children, while Parnell was granted visitation rights, The Philadelphia Inquirer reported.

"I strongly disagree with the ruling today and I'm devastated by the decision," Parnell said in a statement announcing that he would suspend his campaign. "There is nothing more important to me than my children, and while I plan to ask the court to reconsider, I can't continue with a Senate campaign."

A spokesman for Trump, Taylor Budowich, tweeted that Parnell "spoke w/ Pres. Trump and told him of his intention to suspend his campaign given the decision by the PA court."

The Pennsylvania Senate race "remains a top priority for Pres. Trump & the '22 MAGA Map—rallying our movement behind the best America 1st candidate remains critical," wrote Budowich.

Despite Republicans having lost the White House, the House and the Senate under his watch, Trump has emerged as the party's undisputed kingmaker in the 2022 midterms.

But the implosion of Parnell's campaign underscores the potential peril, for Trump and the Republican Party, of his willingness to overlook serious allegations against his preferred candidates.

For Trump, what appears to matter most is whether candidates publicly embrace his fraudulent claims that the 2020 presidential election was stolen from him.

This adherence to Trump's lies about the election has emerged as the primary litmus test for candidates seeking the former president's influential endorsement.

So far in the 2022 midterms, Trump has endorsed at least three Republican candidates in national races who have been accused of threatening or abusing women.

Alongside Parnell, Trump endorsed Georgia Senate candidate and former NFL star Herschel Walker in the Georgia Senate race, another closely watched contest that could tip the balance of the Senate.

In 2008, Walker's ex-wife Cindy Grossman accused him of repeatedly threatening her with guns and knives during their marriage. At one point, Grossman said Walker threatened to kill her while holding a razor to her throat.

Walker did not deny the allegations at the time, but instead he said that in the years since then he has gotten treatment for previously undiagnosed psychiatric disorders.

Trump has also endorsed Ohio congressional candidate Max Miller, a former Trump White House senior aide who was accused by Stephanie Grisham, a Trump press secretary, of slapping and choking her during a fight. Miller denies the accusation.

Asked on Monday whether Trump regretted his decision to endorse Parnell, a spokeswoman directed CNBC to Budowich's tweets.

Trump himself is no stranger to campaigning under a cloud of accusations by women. During his 2016 presidential campaign, more than a dozen women came forward to allege that Trump sexually harassed, abused or assaulted them.

He denied them all, and insisted, as he still does today, that he was the victim of a smear campaign.

"I am a victim of one of the great political smear campaigns in the history of our country," Trump said at a campaign rally in October of 2016.

The comments came shortly after an explosive tape of Trump at an "Access Hollywood" interview was made public, on which he bragged about assaulting women.