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Days after pleading guilty to a charge of misusing campaign funds, Representative Duncan Hunter of California said on Friday that he would resign his seat in Congress “shortly after the holidays,” capping a remarkable downfall for a war hero and onetime rising star of the Republican Party.

Mr. Hunter, who in 2008 was elected to represent a conservative district in San Diego County, where his father served as a congressman for nearly 30 years, had for more than a year been under indictment by federal prosecutors for allegedly spending more than $200,000 in campaign funds on personal expenses.

After pleading guilty on Tuesday, his resignation was widely expected, and on Thursday the House Ethics Committee issued a letter to Mr. Hunter telling him he should not vote on legislative matters. He will be sentenced on March 17 and faces a maximum of five years in prison, although prosecutors have said they will ask for a minimum sentence of no longer than a year.

Despite the charges, Mr. Hunter, who turns 43 on Saturday, won re-election last year, and his departure opens up a crucial congressional seat that Republicans will be challenged to hold in next year’s election. Mr. Hunter’s wife, Margaret, was also indicted and reached a plea deal earlier this year.