Ralph Nader (search) had a testy meeting Tuesday with black members of Congress and rejected their request that he quit the presidential race. At the same time, Arizona Democrats prepared to challenge Nader's qualifications to appear on that state's ballot as an independent candidate.

The developments reflect Democrats' increasing frustration with Nader and his potential to woo liberal votes away from John Kerry (search), the presumptive Democratic presidential nominee.

Shouts could be heard from inside the meeting in the basement of the U.S. Capitol with more than a dozen Congressional Black Caucus (search) members, including Nader's voice, in what proved to be a rancorous session. One female shouted, "You can't win," to which Nader shot back an inaudible response.

Some lawmakers stormed out of the meeting for a House vote and didn't return.

"It became abundantly clear to us that this was about Ralph Nader and we were sorely disappointed," caucus chairman Elijah Cummings, D-Md, said afterward. "If nothing else we believe we've had an impact on his conscience. Now we pray he'll synchronize his conscience with his conduct."

Nader dismissed the shouting as an "exciting exchange" between two sides with the same goal — the defeat of President Bush — but with different strategies for achieving it.

Separately, Democrats in Arizona were expected Wednesday to formally challenge Nader's qualifications to appear on the ballot. Democratic National Committee spokesman Jano Cabrera said the challenge would focus on the validity of thousands of signatures Nader's supporters submitted to Arizona officials.

Cabrera stressed that the state party had not requested DNC resources and that any decision to challenge Nader's ballot access rests with state officials. But he said the national party stands behind the effort in principle.

A spokeswoman for the Arizona Democratic Party would only say that a challenge would be filed Wednesday.

Democrats have complained that Nader's candidacy would siphon votes from Kerry and they have actively sought to discourage voters from supporting him. But this would be the first time any state party has used formal means to try to remove Nader from a ballot.

"We have never been moved by Nader's repeated assertions that it was Al Gore and not he who was at fault for the outcome of the 2000 election and apparently the Arizona Democrats seem unconvinced by his explanation as well," Cabrera said.

Nader said any challenge in Arizona has "a lot of mischief potential" because "there are very partisan Democrats" in the Arizona secretary of state's office.

"If this becomes a pattern of harassment in other states, we will ask John Kerry to disown and disapprove of these antidemocratic tactics," Nader said.

Kerry campaign officials could not immediately be reached for comment.

Nader is not yet on any state ballot. He has been endorsed by the national Reform Party, which has ballot lines in seven states, including the battlegrounds of Florida and Michigan. He also is seeking the endorsement of the Green Party, which has secured ballot access in 22 states and the District of Columbia.

Nader's campaign submitted more than 22,000 signatures to Arizona election officials June 9 — far more than the 14,694 valid signatures required by state law to compete against President Bush and Kerry in Arizona.

That same day, Arizona Democratic Chairman Jim Pederson promised to examine the filing to determine whether the signatures are valid, if the petition drive was conducted properly and if the financing was reported accurately.