Up until about 30 years ago, Texas was a strong Democratic state, and presidential caucuses--the preferred system prior to 1976--were little more than local turf wars between the liberal and the conservative wings of the party establishment. According to Dr. Patrick Cox, Associate Director for Congressional and Political History at the University of Texas, prior to the 1970s, the Texas Democrats used the "unit rule," meaning that all delegates--often under the guidance of the governor--supported one candidate at the national convention. From about 1950 until the mid-'70s, the conservative wing dominated, most notably in the persons of governors R. Allan Shivers and John Connally, Jr.

But in the lead-up to the 1976 presidential nominations, conservative Democrats were concerned that the liberal faction was better organized--and that this would hurt the presidential aspirations of one of their own, then-senator Lloyd Bentsen. They made a forceful push for a primary, which they believed would give an edge to the more popular candidate, instead of the one with the best organization. Unable to roll the liberal wing of the party, the conservatives eventually settled on a compromise, where two-thirds of the pledged delegates (126 total) are decided by primary, and the remaining one-third (67) are decided in caucus. (Bentsen lost to Jimmy Carter anyway.)

The Texas Democratic primary is the only one that allocates delegates by state senate district. (Most use congressional districts). The number of delegates for each of the 31 districts is not apportioned strictly by population; instead, each gets a number of delegates based on past loyalty to Democratic candidates. This year, a district's delegate count is weighted by the percentage of support Chris Bell and John Kerry received in the 2006 gubernatorial and 2004 presidential elections....

Because caucus-goers pledge their support to a specific candidate when they sign in, the Texas caucus functions like a secondary primary. One has to have voted in the primary to participate in the caucus. (As Bill Clinton put it,"[Texas] is the only place in one election that you can vote twice without going to jail.")

It is difficult to predict how many Texans will participate in this stage of the vote. Historically, Texas Democratic caucuses have had abysmal turnouts. This year, however, the caucus will play a key role determining the presidential nominee, and both nominees are actively stressing the importance of caucusing to their supporters. A record turnout is expected.

There are three phases to the caucus: the precinct caucus, which starts 15 minutes after the primaries close; the county convention caucus, held on March 29; and the state convention caucus from June 5-7. But the different stages are mostly a formality; precincts have been told to phone in their election results on the night of March 4, so we should have a good feeling for how many delegates each candidate will receive by Wednesday morning.