(NewsNation) — Vice President Kamala Harris’ campaign said former President Donald Trump is “running scared,” after the GOP nominee announced he would debate Harris on Fox News rather than his previously scheduled ABC debate against President Joe Biden.

Trump posted on his social media platform Truth Social late Friday, saying he agreed with Fox News to debate Harris, the presumptive Democratic presidential nominee, on Sept. 4.

“The Debate was previously scheduled against Sleepy Joe Biden on ABC, but has been terminated in that Biden will no longer be a participant, and I am in litigation against ABC Network and George Slopadopoulos, thereby creating a conflict of interest,” Trump wrote.

Harris on Friday secured the required number of votes for the nomination. The achievement came less than two weeks after President Joe Biden announced he would no longer seek the nomination and endorsed Harris for the role.

“Donald Trump is running scared and trying to back out of the debate he already agreed to and running straight to Fox News to bail him out,” Harris campaign Communications Director Michael Tyler wrote in an official statement. “He needs to stop playing games and show up to the debate he already committed to on Sept 10. The Vice President will be there one way or the other to take the opportunity to speak to a prime time national audience.”

Trump accused Democrats of replacing Biden as the party’s anticipated nominee because he “lost” the first presidential debate in June.

Viewers widely criticized the president’s performance as “disastrous” after he appeared to lose his train of thought and struggle to finish sentences throughout the evening. The debate sparked outcries from fellow Democrats urging the 81-year-old president to drop out of the race.

More party leaders and Democratic donors echoed those concerns after Biden’s solo news conference earlier this month. During his address, Biden confused the name of Ukrainian President Volodymyr Zelenskyy with that of Russian President Vladimir Putin and referred to Vice President Kamala Harris as “Vice President Trump.”

The news conference was a pivotal moment for some Democratic Party members who were on the fence about the president’s ability to serve a second term.

“As everyone knows, the Democrats have Unconstitutionally taken a Candidate, who was acknowledged to be defeated, and unceremoniously replaced him with a new Candidate,” Trump wrote in his post on Friday. “This has never been done before, and is a Threat to Democracy, but I am totally prepared to accept the results of this ‘coup,’ and replace Joe on the Debate stage with Crazy Kamala Harris.”

It’s unclear whether Trump’s comment was a repetition of his false claims that the 2020 election was “stolen” or a reference to the June debate. The Cybersecurity and Infrastructure Security Agency (CISA) found no evidence that any voting system deleted or lost votes, changed votes or was — in any way — compromised.

According to Trump, his suggested Fox News debate would happen Sept. 4 at an undetermined arena in Pennsylvania. Fox News anchors Bret Baier and Martha MacCallum would moderate, and rules would be similar to those of June’s CNN debate.

Unlike that debate, the potential Sept. 4 event would feature a “full arena audience,” Trump said.

However, it’s unclear whether the debate will happen at all. Harris’ campaign hasn’t agreed to attend and is standing firm on plans for ABC’s Sept. 10 debate.

“The Vice President will be there one way or the other to take the opportunity to speak to a prime time national audience,” Tyler wrote. “We’re happy to discuss further debates after the one both campaigns have already agreed to. Mr. Anytime, anywhere, anyplace should have no problem with that unle/promoss he’s too scared to show up on the 10th.”

The disagreement is the latest development in what has, so far, been an unusual presidential campaign season.

As Trump eyes a second term, he’s also cooperating in an ongoing investigation into the July 13 assassination attempt at a Butler, Pennsylvania, rally. He suffered a graze wound to his ear when a gunman opened fire from atop a nearby rooftop. One rally attendee was killed and at least two others were seriously injured in addition to the shooter, whom the U.S. Secret Service shot and killed.

Meanwhile, a virtual roll call vote earlier this week made Harris the nation’s first Black, Asian-American, woman nominee atop a major party ticket.