The parlor game du jour in South Florida these days centers on which Republican brother is more vulnerable to losing re-election in two of the most competitive, and negative, races in the country.

Republicans say Rep. Mario Diaz-Balart appears to be in slightly more danger than his brother, Rep. Lincoln Diaz-Balart, who represents the adjacent 21st district. Democrats largely take the opposite view, saying Mario in the 25th district is more likely to keep his seat than Lincoln is.

Regardless, Republicans are vigorously defending both men, and Democrats are going after the brothers with gusto, targeting them together in a recent TV ad that seeks to tie both to President Bush’s low approval ratings.

“The Diaz-Balart brothers: Loyal to Bush. Not to us,” a Democratic Congressional Campaign Committee ad intones. The spot began airing in English on Oct. 17 and in Spanish on Oct. 21, with the cost of the ad buy estimated at more than $1 million.

Even Republicans acknowledge that’s a powerful message in a year in which the mood of voters is decidedly anti-incumbent, especially anti-Republican incumbent.

“The seats aren’t vulnerable,” one Florida Republican political consultant said. “The climate is vulnerable. … The biggest challenge both incumbents face is Bush.”

One GOP strategist said Mario has not done as good a job as Lincoln has in presenting voters with a clear choice between himself and his opponent, Miami-Dade County Democratic Party Chairman Joe Garcia. Lincoln is facing former Hialeah Mayor Raul Martinez (D) in one of the most expensive and negative races in the country.

“In order for each Republican to succeed in this election, they have to make their campaign about a choice, not a referendum” on President Bush, the strategist said. “In [Lincoln’s district], a clear choice is being presented to voters. The question is whether that is happening in Mario’s district, but there is certainly the potential there to do so.”

Plus, Mario’s district, which has a younger electorate and is more suburban than the 21st, appears “more vulnerable to the national mood,” the Florida Republican consultant said. Polls have consistently shown a tight race between Mario and Garcia, and there’s little question that demographic changes in the district have made it more competitive for the GOP Congressman, who led the state commission that essentially drew the heretofore solidly Republican district after the 2000 Census. But the same is true for Lincoln.

Speaker Nancy Pelosi (D-Calif.) is campaigning in the state and will appear with Garcia and Martinez at a news conference today in the heart of Little Havana.

“This is a whole new day in politics and in no place is it more obvious than Florida,” she said this week, according to the Miami Herald.

Democratic voter registration has outpaced Republicans in both districts — more so in Mario’s district. Also, Hispanic voters in both areas are changing. Cuban voters have begun to shift away from the hard-line anti-Castro stance both brothers have perfected, but those voters are slowly being overtaken by non-Cuban Hispanic voters that largely don’t care about their Representative’s position on U.S.-Cuba policy.

Martinez spokesman Aaron Blye acknowledged the political leanings of the district are changing. The Miami Herald recently endorsed Martinez over Lincoln, but backed Mario over his challenger.

The 25th district has been hit harder than the rest of Florida by the home foreclosure crisis gripping the nation.

Garcia spokesman Andy Diaz said Mario’s support for many of Bush’s economic policies has been a centerpiece of the Garcia campaign.

“He voted 100 percent with Bush,” Diaz said. “That’s his own proactive way of completely alienating himself from the people of his district.”

Meanwhile, Lincoln has successfully driven up Martinez’s negative ratings in a series of hard-hitting negative ads that dredged up the former mayor’s past indictment on corruption charges as well as a physical altercation — caught on tape — with a protester when he was mayor. Martinez was convicted in 1991 of extortion, but that was thrown out by the court. He was retried twice, and both ended in hung juries.

Internal GOP polling has Martinez’s unfavorability rating at close to 50 percent, said Lincoln Diaz-Balart spokesman Carlos Curbelo, who also works with Mario.

Martinez has hit back with ads airing unconfirmed allegations that a Puerto Rican politician delivered a suitcase of money to Lincoln. The former mayor has said that the corruption trials exonerated him, and Blye said the years-old fight with a protester has been taken out of context, given the man, who has a criminal record, allegedly threw rocks at Martinez and police officers.

Mario’s race against Garcia has not been as negative, but he has sought to play up Garcia’s ties to failed energy giant Enron along with the fact that Garcia does not live in the district.

Still, Curbelo said the demographic changes in both districts will not necessarily work against the brothers. Lincoln will be boosted by the fact that many new non-Cuban Hispanic voters have their incumbent Congressman to thank for their voting rights, given his support for a bill during the late 1990s that provided a path to citizenship for many Central American immigrants.

Mario, whose district has the highest concentration of Colombians of any Florida district, should get credit for pushing the yet-to-be passed Colombian free-trade pact, Curbelo said. Plus, Curbelo added, both brothers have a significant advantage already based on absentee ballot requests.

Polls have shown Martinez and Garcia well within the margin of error. But a recent poll done for Univision showed Lincoln with a 14-point lead. Blye said the poll was flawed because the pollster used to work for Lincoln.

Ultimately, Curbelo said, the get-out-the-vote effort being mounted by both brothers will save the day, even as the presidential race in Florida appears to be turning in favor of Democrats.

“If the concern is whether our voters are going to participate intensely, I’m not concerned at all,” Curbelo said.