WASHINGTON — Donald Trump lashed out on Monday at Republicans who have tried to tone down his rhetoric about election fraud, calling his own party’s leaders “so naive” and claiming without evidence that large-scale voter fraud is real.

Trump’s claims were part a Monday morning blast of tweets that took on his party, the women who’ve accused him of sexual misconduct, the media and Vice President Joe Biden.

The defensive barrage comes as Republicans are under pressure to rebuke Trump’s claims that the presidential election is “rigged” in Hillary Clinton’s favor. The GOP push reflects growing worries that their nominee’s unsubstantiated rhetoric could erode public trust in elections and lead to damaging disputes if he loses.

Trump’s running mate, Mike Pence, declared Sunday the ticket will “absolutely accept the results of the election.” But Trump seemed to brush back against his vice presidential pick.

“Of course there is large scale voter fraud happening on and before election day. Why do Republican leaders deny what is going on? So naive!” he tweeted Monday.

There is no evidence to back up Trump’s claim of widespread voter fraud. A study by a Loyola Law School professor found that out of 1 billion votes cast in all American elections between 2000 and 2014, there were only 31 known cases of impersonation fraud.

The Trump tweets show he is still largely focused on issues other than making his case to voters, with just three weeks left and much ground to make up in opinion polls. He is spending much of Monday out of sight before campaigning in Green Bay, Wisconsin, in the evening. Clinton is spending the day Monday with advisers near her home in New York, preparing for the final debate Wednesday night.

As she prepares, her campaign was hit with a new revelation on a persistent problem.

Newly released FBI documents show a senior State Department staffer sought to change the classification level of an email that was on Clinton’s private server. The official, State Department Undersecretary for Management Patrick F. Kennedy, requested the change for an email related to the 2012 attacks on the U.S. diplomatic compound in Benghazi, Libya.

Kennedy said that would allow him to ensure the document was “never to be seen again.” The FBI did not change the classification level.

Clinton’s campaign also continues to answer for hacked emails being released by the thousands by WikiLeaks. The most recent batch showed Clinton generally avoided direct criticism of Wall Street as she examined the causes and responses to the financial meltdown during a series of paid speeches to Goldman Sachs.

WikiLeaks said Monday that founder Julian Assange’s internet access has been cut by an unidentified state actor. Few other details were immediately available.

Clinton’s email trouble has largely been overshadowed by multiple allegations by several women that Trump had sexually assaulted them.

Trump pushed back against those women Monday, tweeting: “Can’t believe these totally phoney stories, 100% made up by women (many already proven false) and pushed big time by press, have impact!”

In another tweet, Trump linked to a video montage of Biden greeting and hugging women at various events. The Democrat has not been accused of sexual improprieties, but has raised eyebrows for his lingering or awkward embraces of women.

Trump’s tweets on voter fraud zeroed in another source of tension among Republicans. GOP leaders often raise the risk of fraud as they make a case for tightening access to the polls through voter identification laws and other restrictions. But Trump’s often repeated claim that the election is “rigged” has put the party in the unusual position of having to express faith in the legitimacy of the election system.

Leaders in both parties fear Trump’s claims will encourage his most ardent supporters not to accept the results, leading to prolonged litigation, possible violence or hardened divisions — or some combination of the three. That could make it even more difficult to govern and could take a long-term toll on the democracy.

Even staunch conservatives have found themselves in the position of trying to gently walk back the nominee’s remarks.

“I just don’t think it’s that constructive to make this a campaign issue,” Rep. Steve King of Iowa said Monday on CNN. He said he shares Trump’s worries about election fraud, but acknowledged Trump’s claims are “partially unsubstantiated.”

“I don’t want to say anything on this program that delegitimizes our election,” King said.

Associated Press Writer Laurie Kellman in Washington contributed to this report.