Reno, Nev. ? John Edwards and Hillary Rodham Clinton criticized Barack Obama’s praise of the Republican Party and Ronald Reagan – an anathema for many Democrats, particularly union members considered crucial to winning Nevada’s Democratic caucuses today.

Obama responded by suggesting Clinton would be a “president whose plans change with the politics of the moment” as part of one of his most direct critiques of the New York senator yet.

The intensity reflects what polls suggest could be a tight contest today as Nevada plays its most prominent role ever in a presidential nominating campaign. Nevada was granted a coveted spot right after Iowa and New Hampshire in an attempt to bring more racial and geographic diversity into the selection.

The novelty means there isn’t a reliable way to determine who is likely to turn out at caucuses across the state. In addition, nine caucuses are to be held in casinos for the first time to allow shift workers to participate on a busy holiday weekend – making the result even more unpredictable.

Obama got a boost when he won the endorsement of the Culinary Workers Union that represents 60,000 housekeepers, bartenders, waiters and other employees on the Las Vegas Strip. Then a judge dismissed an attempt to eliminate the casino caucus sites. But Clinton still holds an edge in most polls.

Edwards, his chances for the presidency diminished by losses to Obama in Iowa and Clinton in New Hampshire, did not run television ads in the state and did not plan to stay in Nevada to wait for results.