President Trump tweeted that Sen. Kirsten Gillibrand (D-N.Y.) “would come to my office ‘begging’ for campaign contributions” and “would do anything for them.” (Jabin Botsford/The Washington Post)

President Trump on Tuesday attacked Sen. Kirsten Gillibrand (D-N.Y.) in a tweet widely criticized as being sexually suggestive, sparking outrage at a time when the nation is reeling from a wave of accusations about improper behavior by powerful men — including Trump himself.

In his morning tweet, Trump referred to Gillibrand as a "lightweight" and a "total flunky" and said that, when he was a New York real estate developer, she "would come to my office 'begging' for campaign contributions" and "would do anything for them."

The tweet, targeting a female senator who has called on Trump to resign for his past behavior, came as the president faces renewed scrutiny of claims of sexual harassment and assault that surfaced during the campaign. Trump has denied all the claims, accusing the women of lying.

His attack on Gillibrand prompted a swift backlash on social media and on Capitol Hill, where Democratic calls increased Tuesday for Trump to either resign or face congressional investigations of his actions.

Gillibrand, who is often mentioned as a potential 2020 Democratic presidential candidate, called Trump's tweet "a sexist smear attempt to silence my voice."

"You cannot silence me or the millions of women who have gotten off the sidelines to speak out about the unfitness and shame you have brought to the Oval Office," she said in reply to Trump on Twitter, later reiterating to reporters her call for Trump to resign.

White House spokeswoman Sarah Huckabee Sanders disputed the characterization of Trump's tweet as sexually suggestive, telling reporters that "there's no way this is sexist at all" and later adding: "I think only if your mind is in the gutter would you have read it that way."

Sanders said Trump was trying to make a point about the corrosive nature of money in politics and characterized Gillibrand as "a wholly owned subsidiary of people who donate to her campaign."

"He's used that same terminology many times in reference to men," Sanders said of the language in Trump's tweet.

By Tuesday afternoon, six Democratic senators had called on Trump to step down, and more than 100 House Democrats had signed onto a letter calling for a congressional investigation.

Sen. Mazie Hirono (D-Hawaii), the latest senator to call on Trump to resign, cited the president's tweet as part of her reasoning, calling the president "a misogynist, compulsive liar, and admitted sexual predator."

"Attacks on Kirsten are the latest example that no one is safe from this bully," Hirono added. "He must resign."

Sen. Elizabeth Warren (Mass.) was among the other Democratic senators to rally around Gillibrand, asking Trump on Twitter whether he was trying to "bully, intimidate and slut-shame" Gillibrand.

"Do you know who you're picking a fight with?" Warren wrote. "Good luck with that, @realDonaldTrump."

A Republican consultant close to the White House declined to defend the content of Trump's tweet, but said it was drafted with the aim of becoming the water-cooler conversation of the day and diverting attention from his accusers.

"It's a better conversation for him than for the women who are accusing him to be dominating the conversation," said the consultant, who requested anonymity to speak more candidly. "He's drowning out those voices."

Trump's tweet also largely overshadowed a White House event at which he signed a $700 billion defense budget that seeks to increase military spending and operational capabilities, a major priority for his administration. And it came on the eve of a tax speech that the president plans to deliver Wednesday about what could be his first big legislative win.

Trump began Tuesday with a separate tweet accusing Democrats of focusing renewed attention on his alleged misconduct out of their supposed frustration that investigations into Russian meddling in the 2016 presidential election are not harming him.

"Despite thousands of hours wasted and many millions of dollars spent, the Democrats have been unable to show any collusion with Russia — so now they are moving on to the false accusations and fabricated stories of women who I don't know and/or have never met. FAKE NEWS!" Trump posted.

Trump has repeatedly denied the accusations against him, but the idea that he does not know or has not met any of the women who have accused him of sexual misbehavior is false. The list of women includes a former contestant on his reality show "The Apprentice," a former business partner, a woman who has a photo of the two of them together, a contestant in one of his pageants and a People reporter who interviewed him.

During her White House briefing, Sanders said Trump's denial of knowing the accusers was limited to three women who appeared in a joint television interview and news conference Monday, renewing their public push to gain attention for their stories.

Gillibrand was attending a bipartisan Bible study Tuesday morning when Trump's tweet landed, and her phone was immediately filled with supportive and befuddled messages, wondering just what the president was thinking, a Gillibrand aide said.

In his tweet, Trump offered no evidence to support his claim that Gillibrand had gone to him "begging" for campaign donations "and would do anything for them." According to OpenSecrets, a nonprofit website that tracks campaign contributions, since 1996, Trump has donated $8,900 to Senate Minority Leader Charles E. Schumer (D-N.Y.) and $5,850 to Gillibrand.

Gillibrand met with Trump once in 2010, the Gillibrand aide said, and Trump's oldest daughter, Ivanka, who has tried to cast herself as a champion of women, attended the meeting as well.

Asked about her interactions with the president, Gillibrand told reporters that Trump was "just a supporter — a supporter of my first campaign."

Tuesday afternoon, Gillibrand cited the president's tweet in an email solicitation to raise money for her 2018 reelection campaign.

Over her nearly nine years in the Senate, Gillibrand has focused on issues of equal rights — for gay men and lesbians, transgender people and women.

Trump's attack plays right into her portfolio. Her reelection campaign has drawn no serious opponent, and with speculation that she will renege on her vow not to run for president in 2020, the attack may do her more political good than harm.

In a tweet, Brian Fallon, a spokesman for Hillary Clinton's 2016 presidential campaign, called Trump's tweet "disgusting" but also noted, "It will make the Gillibrand folks ecstatic," implying that the sparring with Trump would raise her profile among what is expected to be a crowded field of Democratic contenders in 2020.

Gillibrand, however, does have detractors within the party. After she said in November that Bill Clinton should have resigned as president following his affair with White House intern Monica Lewinsky, longtime Hillary Clinton adviser and confidant Philippe Reines excoriated her on Twitter for being ungrateful and two-faced.

"Hypocrite. Interesting strategy for 2020 primaries. Best of luck," Reines wrote.

Trump's attack on Twitter coincided with a previously scheduled event Tuesday led by 59 female House Democrats, who formally called on the House Oversight and Government Reform Committee to launch an investigation into allegations of sexual misconduct by the president.

The oversight panel has the broadest subpoena power and investigatory mandate of any congressional committee. The female lawmakers had requested the investigation in a letter to the committee Monday.

Late Tuesday, Rep. Trey Gowdy (R-S.C.), chairman of the oversight committee, said in a letter back that most of the allegations against Trump would constitute state-level crimes and that his committee does not have jurisdiction to prosecute crimes. He said he was forwarding the letter to the Justice Department.

Besides Gillibrand and Hirono, four male senators have called on Trump to resign: Cory Booker (D-N.J.), Jeff Merkley (D-Ore.), Ron Wyden (D-Ore.) and Bernie Sanders (I-Vt.).

Speaking to reporters, Schumer defended his New York colleague, calling Trump's attack "nasty" and "unbecoming" of the presidency.

But he declined to join other Democrats in calling for a formal investigation of allegations of sexual misconduct by Trump. Schumer added that the president should "cut it out with the tweeting. He ought to stop tweeting and start leading."

Senate Majority Leader Mitch McConnell (R-Ky.) declined to say whether Congress should investigate the allegations against Trump, saying that "we're focused on the Senate" and that his chamber's ethics committee can investigate only allegations against senators.

"What we're in charge of here is the Senate," McConnell told reporters.