Politico, the Web site devoted to covering all facets of the political news cycle, said late on Thursday that it had suspended one of its White House reporters for making numerous disparaging and vulgar comments about Mitt Romney.

The reporter, Joe Williams, had a history of describing Mr. Romney and other conservatives in provocative terms on his Twitter feed. And on Thursday, after Mr. Williams appeared on MSNBC and said that Mr. Romney only appeared comfortable around “white folks,” Politico said that it had taken action.

In a memo to the staff, the Web site’s editors said his comments were regrettable and inappropriate.

“Our standards are serious, and so are the consequences for disregarding them. This is true for all Politico journalists, including an experienced and well-respected voice like Joe Williams,” the memo said.

In messages posted to his Twitter account, Mr. Williams ridiculed Mr. Romney in a variety of ways. He alluded to the now infamous Romney road trip to Canada with their dog strapped to the roof and poked fun at Mr. Romney for being out of touch. (“Jeeves knows my tastes,” he wrote in response to a remark Mr. Romney had made about food.) And when Ann Romney commented once that her husband was more relaxed than his public persona would suggest (“I guess we’d better unzip him and let the real Mitt Romney out!” she said), Mr. Williams fired off a crude anatomical joke.

Mr. Williams’s comments caught fire on conservative blogs after Breitbart.com published them along with a clip of the MSNBC appearance. The Washington Free Beacon also published a fuller version of the exchange, which appeared on Martin Bashir’s show.

Referring to Mr. Rommey’s frequent interviews on Fox News, and on the morning program “Fox & Friends” in particular, Mr. Williams said the candidate had a problem relating to people who weren’t like him. “When he comes on ‘Fox & Friends,’ they’re like him. They’re white folks who are very much relaxed in their own company,” Mr. Williams said.

With his comments, Mr. Williams became the latest journalist to breach the quickly eroding line between reporters’ private political thoughts and their duty to present the news dispassionately. Twitter in particular has posed a host of problems for news organizations, which have struggled with how to handle a medium that thrives on being unedited and instantaneous.

A Tweet-first, think-later mentality has become the norm among many journalists, who see Twitter as an outlet for fleeting, unvarnished observations, and not as something that requires the same level of discretion and caution they would ordinarily apply to a news story.

But reporters like Mr. Williams are discovering that no matter how much they try to qualify their Tweets with disclaimers like “These views do not represent my employer,” media consumers see little distinction between personal and professional.

The presidential campaigns now monitor reporters’ feeds closely and often will use any impolitic or indiscreet remark to their advantage. Just this week, the Obama campaign issued a news release full of reporters’ Twitter commentary on a conference call hosted by the Romney campaign. Reporters complained that the call was a “waste of time” and that the Romney campaign seemed unprepared for questions about Mr. Romney’s position on immigration.

Mr. Williams’s Twitter feed was locked on Friday morning, making it impossible for the general public to view his previous messages.

The memo to the Politico staff is below: