The Catholic voter, 64 million strong, is the elephant in the room.
Since 1972, Catholics have ended up supporting the popular vote winner -- Democratic or Republican -- in every presidential election.
Other demographic groups do not generally vote for the presidential winner. Blacks and Jews always support Democrats; white Protestants and evangelicals support Republicans; and union members vote Democratic. Sometimes the Democrat wins and sometimes the Republican wins.
Catholics swing both ways.
It didn't used to be this way. American Catholics used to be reliable Democratic voters, attracted by the Democrat's compassion for the working class and the poor. For most of the 20th Century, there was a strong leftist -- "Social Justice" -- Catholic tradition exemplified by the Jesuit Berrigan brothers.
Nowadays, Catholics that go to Mass regularly vote Republican, while those who go irregularly, vote Democratic -- a voting pattern similar to church goers and church skippers in general.
In Ohio and Pennsylvania, Catholic voters tend to be older, white working class, blue-collar union members -- Germans, Italians and Irish.
In Texas the key Catholic voters are Latinos. Blacks make up 12% of the population, Latinos 36%.
What does this mean for Hillary's chances? In the recent primaries in California, Nevada, Massachusetts, New York, Connecticut, and Florida, Catholic voters supported Clinton over Obama by a 2-1 margin, according to the exit polls.
But in the latest primary in Wisconsin, Catholics voted 50-50 for each candidate, which might be a harbinger of a more even split in the upcoming primaries, favoring Obama.
If Clinton can hold two thirds of the Latino Catholic vote, she will probably win in Texas. Obama supporters claim that his Latino support is rising and that Latinos will not vote as enthusiastically as blacks.
But their hopes may not be fulfilled. The most recent Belo Tracking Poll today noted "What was a 29-point gap in favor of Hillary Clinton among Hispanics yesterday (61%-32%) has climbed to a 40-point gap for Clinton (67%-27%)." One commentator has said that Clinton's liberal Methodism dovetails with many Catholic teachings.
In the last two general elections, the Hispanic vote was significant in George Bush's wins in 2000 (35%) and 2004 (41%). In contrast, the last Republican candidate, Bob Dole, won only 21% of the Hispanic vote in his losing 1996 campaign.
"Hispanics loom as a potential swing vote in the presidential race because they are strategically located on the 2008 electoral college map. Hispanics constitute a sizable share of the electorate in four of the six states that President Bush carried by margins of five percentage points or fewer," according to a Pew Study. These states -- New Mexico with a 37% Hispanic electorate, Florida with 14%, and Nevada with 12% -- are going to be closely contested this year.
If Obama can win these two groups of Catholics -- Reagan blue-collar union voters and Latinos, which Clinton has been winning -- then he will have a clear shot at the nomination and the tea leaves will bode well for his success in the general election.
If Obama fails to win this key swing vote, Democratic insiders will be worried. This blue-collar/Latino vote may well go to McCain, who has been doing well with Catholics during the Republican primaries. McCain's compassionate stance on immigration may turn out to be a real boon for Republicans among Latinos.
We can be sure that in the coming general election, the Republicans will once again trot out Rovian anti-abortion, anti-gay issues to whip Catholics into line. Abortion and gay marriage were deliberately exploited -- in presidential races where they don't really belong -- as the wedge issue to split Catholics from the Democrats.
But things seems to be looking good for the Democrats. In the 2006 midterm elections the Democrats were able to capture the Catholic vote by 55% to 45%. This is a 7% point loss for the Republicans, in sharp contrast to 2004, when Republicans got 52% versus 47 % for the Democratic vote.