WASHINGTON — Ivanka Trump said on Monday that her father felt “very vindicated” by the testimony last week of James B. Comey, the ousted F.B.I. director, who, under oath, accused President Trump of firing him for his handling of the investigation into whether the Trump campaign colluded with Russia to sway the election.

“My father felt very vindicated in all the statements that he’s been making, and feels incredibly optimistic,” Ms. Trump, a senior adviser to the president, said in an interview on “Fox & Friends.”

Her comments were the latest effort by a White House in crisis to discredit and play down the significance of the account Mr. Comey gave on Capitol Hill, in which he strongly suggested the president had tried to obstruct justice in imploring him to drop an investigation into his former national security adviser’s contacts with Moscow and requesting the F.B.I. director’s personal loyalty.

Mr. Trump said in a news conference on Friday that Mr. Comey had lied about those conversations, and he asserted that Mr. Comey’s account proved that there had been no collusion between the campaign and Russia, nor any attempt to obstruct an investigation. Over the weekend, Mr. Trump took to Twitter to suggest that Mr. Comey’s move to work through a friend to share with a reporter the contents of contemporaneous memos he kept of his exchanges with the president might have been illegal, and he called the act “cowardly.”