He added: “When the Democrats try and defend him, it’s a disgrace to our country. They can’t do that. And let me tell you, it’s not working politically very well for them.”

Still, the confused messaging from Mr. Trump and his top officials after the most high-stakes decision of his presidency threatened to undercut the message the administration was sending to Iran, experts said.

And that message was further undercut by other tweets that Mr. Trump sent on Monday morning. One of them included a photoshopped image of Senator Chuck Schumer and Speaker Nancy Pelosi wearing a turban and a head scarf in front of an Iranian flag, claiming it showed “the corrupted Dems trying their best to come to the Ayatollah’s rescue #NancyPelosiFakeNews.”

The retweeted image was the most extreme version of a sentiment that the president spent the morning advancing by retweeting criticism of Ms. Pelosi, and suggesting that she was a supporter of the Iranian government.

Ms. Pelosi has criticized the Trump administration for the killing of General Suleimani, saying it risked a “dangerous escalation of violence” and was based on questionable intelligence.

The president’s stream of Twitter posts targeting her appeared to be an attempt to assail her credibility the same week she was expected to send two articles of impeachment against Mr. Trump to the Senate. The tweet was also a reminder of the way Mr. Trump has in the past harnessed fears of Muslims and terrorism for his own political purposes.

Responding on Twitter, Mr. Schumer asked, “President Trump: How low can you go?”

Dana Shell Smith, a former United States ambassador to Qatar, wrote on Twitter that Mr. Trump was engaging in “hate speech against an entire religion.”