In an unusual move, the Club for Growth announced Friday that it will oppose Sen. Bob Bennett's (R-Utah) reelection, without specifying a candidate it might support.

A series of candidates are looking to upend Bennett in a May party convention or, failing that, in a June primary. In a release, the Club doesn't mention any of them, but assures it will oppose Bennett, regardless.

“Bob Bennett is out of touch with the times and with his state, and Utah Republicans have better choices for their candidate in November,” Club President Chris Chocola said.

“Our extensive research into the race suggests Utah Republicans already understand this, as they have begun rallying around several viable and superior candidates,” he continued. “The Club for Growth PAC is committed to seeing one of them defeat Bennett either at the nominating convention in May or in a primary election in June.”

The release makes official what has already been a very public effort from the Club against Bennett. It already has run ads against the senator and contacted potential delegates to the state convention.

The Club could simply work against Bennett and then hop on board with whichever candidate emerges as his top competition. Bennett's opponents will try to prevent him from getting 60 percent of the vote at the convention, which would hand him the nomination. If no candidate gets 60 percent, then the top two go to a primary.

Attorney Mike Lee recently entered the race, and former congressional candidate Tim Bridgewater and activist Cherilyn Eagar are also running.

A couple of better-known Republicans, state Attorney General Mark Shurtleff and businessman Fred Lampropoulos, have aborted their campaigns.

The race represents the second major GOP Senate contest on which the Club is weighing in. It is also backing Marco Rubio over Gov. Charlie Crist in Florida.

UPDATE: A source says the Club feels particularly good about its odds at the convention, where it thinks any of the three opponents mentioned could fill the void an pick up anti-Bennett votes. The multi-ballot process will gradually narrow the field, and any of the three could emerge as that one main challenger.

In advance of that convention, the Club will work the March caucuses, where convention delegates are chosen. And it thinks it might even be able to knock Bennett off at the convention.