AUSTIN, Tx. – Barack Obama has a secret weapon in Tuesday’s Democratic primary in Texas, pretty well-known in these parts: George W. Bush.

Not that the current president is trying to help the man who criticizes him at every turn.

But Bush’s electoral appeal among home-state Hispanics four years ago, combined with his failure to generate significant black support, complicates Hillary Rodham Clinton’s drive to put a significant dent in Obama’s lead in the race for delegates.

Even if she wins the popular vote – polls show a close race – the former first lady faces additional obstacles, and could wind up with fewer Texas delegates than her rival.

For one, there is the national Democratic Party’s aversion to winner-take-all contests.

Then there is a unique same-day primary and caucus system known as the Texas Two-Step.

Until two decades ago, the primary was advisory only, and all delegates were picked in caucuses. But in 1988, “a group of reformers wanted to put a primary into the process to enhance participation,” according to Ed Martin, a former executive director of the party.

“But they also wanted to maintain elements of the caucus … system to the process. The theory was that’s a way to bring all the new people in and get them involved” in building the party, he said.

Bottom line, 126 delegates at stake in the primary on Tuesday, 67 more in caucuses that convene 15 minutes after the polls close, and more than enough complexity to go around.

“I think we have to maintain our (national) delegate lead and make sure that we don’t get blown out in” Texas or Ohio, another state voting Tuesday, says Obama. He leads Clinton by 109 delegates overall in The Associated Press’ count, and 151 among those elected in primaries and caucuses.

“In the final analysis this is all about a delegate count,” says Henry Cisneros, a Cabinet officer under President Clinton, and a supporter of the former first lady. “There’s a scenario where you could win an election and get swamped in the caucuses.”

The primary is actually 31 separate contests, one in each of the state’s state Senate districts, with anywhere from two to eight delegates divided between winner and loser.

That’s where Bush, blacks and Hispanics come in.

The 126 primary delegates are distributed across the state based in part on the number of votes cast in the 2004 presidential and 2006 gubernatorial elections, rather than strictly on population.

State senate districts that gave Sen. John Kerry or the 2006 gubernatorial candidate, Chris Bell, a majority or even a sizable minority in their votes in 2004 and 2006 are favored with more delegates under the formula. That generally means areas that are home to blacks and liberals, in areas around Houston, Dallas and Austin, for example – groups that have strongly favored Obama.

Election day polls in Texas from four years ago show blacks gave Kerry 83 percent of their votes in 2004, to 17 percent for Bush. Two years later, Bell claimed 63 percent black support in losing a four-way race to Republican Gov. Rick Perry.

By contrast, Kerry split the Hispanic votes with Bush, 50-49. Bell got less than that, 41 percent.

As a result, some state Senate districts with heavy Hispanic populations, including areas around Brownsville and Corpus Christi, have relatively few delegates at stake in this year’s presidential primary.

That’s unwelcome news for Clinton, who has won strong support from Hispanic voters in other states.

She faces other Texas obstacles in eroding Obama’s national delegate advantage.

Within each state Senate district, delegates are awarded in rough proportion to the popular vote. That presents a daunting challenge to any candidate hoping to sweep most or all the delegates and run up a big lead.

Of the 31 state Senate districts, 15 have four delegates apiece. Under party rules, unless the winner gains nearly 63 percent of the vote, Clinton and Obama will each walk away with two delegates, and neither will gain ground.

Another nine districts, scattered around the state, have three delegates apiece. The odds overwhelmingly favor a 2-to-1 split, since the winner would have to gain more than 83 percent of the vote to score a 3-0 sweep.

One district, in West Texas, has two delegates, and the winner there would need 75 percent of the vote to win both.

Two districts have five delegates apiece. The likeliest outcome is a 3-2 delegate split, since the winner will need 70 percent of the vote to get a 4-1 victory.

Two more districts each have six delegates. But the winner needs 75 percent of the vote for the winner to gain more than a 4-2 split.

A district in Houston offers seven delegates, and the odds favor a 4-3 split.

The state Senate district with the most delegates, eight, is centered on Austin. The winner there needs slightly over 56 percent to gain even five of the eight, and nearly 69 percent of the vote to gain a 6-2 split.

Most states that hold primaries award a delegate bonus to the winner of the primary vote in rough proportion to the popular vote.

But not Texas.

In effect, the caucuses replace that system, adding yet another level of complexity and competition.

Only primary voters are eligible to participate in the caucuses, one of which will be held in each of the state’s 8,247 precincts.

Each caucus will elect one delegate to attend county conventions for every 15 votes the precinct cast for Bell in 2006, when he won the black vote easily, but trailed among Hispanics.

That will eventually lead to a state convention on June 6 where Obama and Clinton divide the 67 national delegates.