Representative Adam B. Schiff, who became the Democratic nominee for an open Senate seat in California last week, denied on Sunday the suggestion that his primary had been rigged.

Mr. Schiff said that Democrats had swiftly rebuked an assertion from one of his primary opponents, Representative Katie Porter, that wealthy donors had spent millions of dollars for Mr. Schiff to “rig” the race, contrasting his party and former President Donald J. Trump’s false claims around the legitimacy of the 2020 presidential election.

“That term ‘rigged’ is a very loaded term in the year of Trump,” Mr. Schiff said in an interview on NBC’s “Meet the Press.” “It connotes fraud, ballot stuffing and false claims like those of Donald Trump. I think what’s remarkable is Democrats very quickly rallied to say, ‘No, we don’t use that language.’”

Ms. Porter, one of Mr. Schiff’s two progressive primary opponents for the seat, thanked her supporters on social media last week and went on to describe “an onslaught of billionaires spending millions to rig” the primary.

Her remarks drew immediate criticism from Democratic colleagues, including Senator Alex Padilla of California, who dismissed Ms. Porter’s suggestion as “ridiculous” in an interview with Politico.

“That is a sharp contrast to how the Republican Party treats allegations of rigged elections,” Mr. Schiff added on Sunday, referring to Republicans who have characterized the prosecutions after the Jan. 6, 2021, attack on the Capitol as political retribution. “Indeed, they’re urging President Trump to pardon the Jan. 6 insurrectionists if he ever got a chance.”

Ms. Porter failed to advance in the Senate primary last week after Mr. Schiff and his allies spent tens of millions of dollars airing television ads that described Steve Garvey, the Republican opponent, as “too conservative for California.”

Mr. Schiff’s ads have been widely understood to be part of his campaign strategy to draw more Republican voters to the polls to box out his Democratic rivals in California’s “jungle” primary, where the two top finishers advance to the general election regardless of their party affiliation.

The ads drew sharp criticism from Ms. Porter, who characterized them as “brazenly cynical.”

Mr. Schiff defended his campaign strategy during the Sunday interview, saying he simply went after his Republican opponent as his Democratic colleagues did.