Not everyone wants to admit it, but having a Libertarian on the ballot tends to favor the Democrat in a close race, taking a few percentage points away from Republican candidates and allowing Democrats to squeak by. And that party's November slate could give an edge to Democrats in more than a dozen races.

Having a thumb on the scale helps. Need an illustration? Look at the fight the Democrats and the Republicans are having over whether to allow Green Party candidates onto the Texas ballot. The Greens — who tend to pull hard-left votes from Democrats and throw tight races to Republicans — can't get on without enough signatures on petitions, so Republican lobbyist Mike Toomey, Gov. Rick Perry's former chief of staff, paid someone to get that done. The Democrats are in court saying the ultimate efforts were illegally financed with corporate money and asking that the petitions be tossed and the Greens kept out. (Libertarians are on the ballot because they got enough support in the previous elections to avoid the petition process.)

It's impossible to know just which races will be close in November. But more than a dozen House races that are on the target lists of either the Republicans or the Democrats have Libertarians in them. Republicans have set their sites on state Reps. Mark Homer of Paris, Donna Howard of Austin, Diana Maldonado of Round Rock, Joe Moody of El Paso, Joe Heflin of Crosbyton, Chris Turner of Burleson, Allen Vaught of Dallas, Ellen Cohen of Houston and Hubert Vo of Houston, among others. Democrats are gunning for state Reps. Tim Kleinschmidt of Lexington, Charles "Doc" Anderson of Waco, Linda Harper-Brown of Irving, Joe Driver of Garland, Dwayne Bohac of Houston and Ken Legler of Pasadena. That's not the entire target list for either party, but those are the races that could be close — and that have Libertarians on the ballot. Libertarian candidates signed up for the two Texas congressional seats on the GOP's national target list, those held by U.S. Reps. Chet Edwards of Waco and Ciro Rodriguez of San Antonio. And they've got statewide candidates all lined up, too.

"In a year like this, I would do anything I could to make it a one-person race," says Todd Olsen, a consultant working with Associated Republicans of Texas, a political action committee trying to preserve and increase GOP majorities in the statehouse. "If I could get the Libertarian to drop out and support me, I'd do it. The Green? I'd do it."

Republican Larry Gonzales, challenging Maldonado in Williamson County, was a political consultant for years before becoming a legislative candidate. He's not willing to concede that Charles McCoy, a Libertarian, is a gift to the incumbent. "There are so many variables," he says. "I think it's really hard to cast a generalization over. ... I just tell candidates, 'Keep your head down and keep going."

Corbin Casteel is a Republican political consultant, too, but he's not on the ballot. He's got no doubt about how Libertarians affects his candidates — they drain votes. "Of course they do," he says. He's helping Republican Jason Isaac of Dripping Springs, who's challenging Democratic incumbent Patrick Rose for a seat in the Texas House. And though they haven't made a public splash about it yet, the Libertarian in that race, Tom Gleinser, decided not to run after two unsuccessful tries. He's endorsing Isaac, according to his website. "The only purpose my being a candidate has served is to help get a Democrat elected State Representative to the 45th district of Texas," he says on his website. "That is bad for the State and bad for the country. ... I have therefore taken the necessary steps to withdraw from being a candidate for office." And he closes his message by endorsing Isaac. That makes it a two-man race.

This has been going on for years, but it's heated up in recent election cycles, which featured a number of very close contests — contests where Libertarians had deciding influence. In the 2004 elections, Austin Democrat Mark Strama won a closely contested race against Republican Jack Stick, getting only 48.6 of the vote but winning, in part, because Libertarian Greg Knowles got 3.7 percent and denied Stick another term in the House. Democrats, who lost several races in that and previous cycles by close margins, took note.

"In a race where you win by less than a percent, everything matters," Strama says now. It didn't hurt to have Knowles on the ballot that year, but everything else mattered, too. You have to bring a race close enough to win, and then hope everything goes right. "Each variable is necessary, but not sufficient," he says.

If he had another close race, would he rather have a Libertarian there as a buffer or not? "Probably so," Strama concedes. "But I would never consider myself sophisticated enough to orchestrate it."

Republicans stand accused of trying to engineer Green alternatives to Democrats on the ballot. But after the Strama race, the Democrats did a pretty good job of exploiting the Libertarian alternative to the Republicans.

In state House races in 2006, Chuck Hopson — then a Democrat — got 51 percent and won re-election to the Texas House; Libertarian Paul "Blue" Story pulled almost 3 percent, leaving only 46 percent for Republican Larry Durrett. Austin Democrat Valinda Bolton just topped a majority in her race with Republican Bill Welch, while Libertarian Yvonne Schick was pulling 4.2 percent of the vote.

Those were closer to 50 percent than the winners might have wanted to be, but still over the magic line. In other House races, the winner got home with less than half the votes. Libertarians got the rest, allowing the winners to take office with something less than majority support.

That year, former state Rep. Robby Cook, D-Eagle Lake, beat Republican Kleinschmidt by 415 votes out of 40,148 cast, winning re-election in 2006 with 49 percent of the vote. Libertarian Rod Gibbs had 1,283 votes, or more than 3 percent. Other Democrats won with under 50 percent, thanks to Libertarians, including Corpus Christi's Juan Garcia, Joe Heflin of Crosbyton, Paula Hightower of Arlington and Joe Farias of San Antonio.

The 2008 election cycle had some similar results — not always losses for the Republicans, but closer races than they wanted or expected. Democrat Wendy Davis unseated veteran state Sen. Kim Brimer, R-Fort Worth. Hopson won his House seat again, barely, pulling less than 50 percent. Lenard Nelson was back in that Corpus Christi House race, but the Libertarian didn't win enough votes to keep the district in Garcia's hands, and Republican Todd Hunter made it over the 50 percent mark. Harper-Brown won re-election with a margin of less than two dozen votes out of almost 41,000 cast. At least two Democrats — Kristi Thibaut and Allen Vaught — won with skinny margins, barely over 50 percent. A Libertarian in Vaught's race gave him a little insurance. Thibaut, who won by about 500 votes, could probably have slept easier with a Libertarian in her race.

"I've run with a Libertarian on the ballot and won, and I've run without a Libertarian on the ballot and won," Bolton says. There were rumors that the Republicans talked a Libertarian out of her 2008 race. She won anyhow (and they're going after her again, blaming her win on a surge of support for Barack Obama that won't be there for her this year). Do Libertarians have any effect? "I've thought about it. A lot. I don't honestly know," Bolton says. "I understand what the conventional wisdom is, and I understand that there are people out there who don't feel comfortable in either party."