Rivals to former Vermont Gov. Howard Dean (search) are wondering about the 2004 Democratic presidential candidate's ability for straight talk, one day after he appeared on a fictional television show being coached with a line that he ended up using in a real live debate.

In a case of art imitating life, Dean last Tuesday delivered one of the most memorable lines of the Democratic presidential debate when he was asked about his capacity to serve the needs of African-American people even though he comes from a state with very few African-Americans.

"If the percent of minorities that's in your state has anything to do with how you can connect with African-American voters, then Trent Lott would be Martin Luther King," Dean responded, referring to the former Senate majority leader who was forced to resign last year for remarks he made suggesting that he supported the late Sen. Strom Thurmond's racial segregation presidential platform in 1948.

But Dean's comeback wasn't as spontaneous as his staff later suggested. In fact, it came from former Clinton campaign adviser and television anchor James Carville (search), who suggested the line in a debate practice one day earlier.

The only issue is that the debate prep was taped Monday for the new HBO series "K Street," which Dean had agreed to participate in as himself seeking assistance from Carville, who also appears as himself in a fictional role as a lobbyist and public relations consultant.

In the story, Carville calls on Paul Begala (search), the real-life former Clinton aide and Carville business partner, who plays himself providing campaign consulting advice to Dean, who is preparing for a debate the following day.

HBO premiered the show Sunday night after a Friday sneak preview for Washington insiders.

In the series, Carville told Dean: "If the percentage of black folks in your state was determinative of your record on civil rights, Trent Lott would be Martin Luther King."

The show later airs real footage from the debate of Dean making the statement, followed by a shot of Carville apparently in the audience laughing at hearing his line. Carville did actually attend Tuesday night's debate and was spotted laughing — as most of the audience did — when the line was spoken.

Carville said he and Begala agreed that as part of the series, which is shot and produced by George Clooney and Steven Soderbergh, they would conduct the debate prep as though Dean were an actual client.

Carville told Fox News at the sneak preview that the debate prep scene was utterly impromptu, ad-libbed and not scripted. He said he had no idea that Dean would use in the actual debate any of the lines from the fictional debate prep taped for a commercial television show.

And that wasn't the only line Dean used from the mock debate prep. He told the audience at Morgan State University, a historically black university: "I'm the only white politician that ever talks about race in front of white audiences."

The line — a claim that North Carolina Sen. John Edwards complained is patently false — is nearly identical to one he said in the "K Street" scene.

Now the question is being asked whether the use of the lines will reflect badly on Dean, who has campaigned as a Washington outsider, anti-establishment candidate who only speaks the truth with straight talk regardless of the consequences. Critics also wonder whether through the taping of a fictional debate prep, Dean actually received free professional advice from some leading Washington insiders.

The day after the debate, the Dean campaign was asked whether the "Trent Lott" line said by Dean during the Congressional Black Caucus Institute debate was his original thinking. One of Dean's aides responded that his boss had offered it up as an off-the-cuff remark. 

The aide's remark was printed in Washington newsletters and said to have been picked up by Carville and HBO's producers, who apparently sent word to the campaign to be cautious about claiming credit for something that they have on tape as an improvisational thought by Carville.

The Dean campaign later acknowledged that it was mistaken in saying it was Dean's line, and suggested that criticism of such missteps is a sign of desperation on the part of rivals who are unable to stop Dean's forward momentum.

Dean Refuses One-on-One With Kerry

Whether he borrowed the debate lines or not, Dean and his campaign have no shortage of zingers about Massachusetts Sen. John Kerry, whom Dean has frequently complained is insulting him behind his back but refuses to say criticism to Dean's face.

On a morning interview program Sunday, Kerry challenged Dean to a one-on-one debate. Later asked whether he would take up the challenge, Dean said he didn't think Kerry should get a special deal.

"John will have five opportunities and many, many more to say what he has to say to my face, and I am looking forward to it. I don't think he gets to condense this to a two-man race. Let's let the public do that," Dean said.  

On Monday, Kerry responded that Dean's word is about as good as his acting.

"Once again, he's going back on something that he talks about. It seems to be a practice," Kerry said. "If you're going to hold yourself out as a straight talker, let's do it."

Over the last two weeks, the Dean campaign has faced increasing criticism and questions of authenticity that have meant to slow the buzz around the front-runner. Some critics have said that the sense is emerging on the campaign trail that the buzz around Dean is no longer helping him. But others say all the discussion about Dean's appearance on the HBO show is potentially helpful to both HBO and Dean.

Carville told Fox News that he has some criticisms of Dean's candidacy, but would not comment about the Dean campaign's statement that the one-liner was original.

Fox News' Carl Cameron contributed to this report.