Sen. John Cornyn’s Facebook friends aren’t in a very friendly mood. The Texas Republican’s page on the popular social networking website has been filled with comments like this one from a Florida real estate broker: “As soon as I read of your endorsement of Charlie Crist, I sent in a donation to the Marco Rubio campaign.”

A new Facebook group has since cropped up challenging members to give “not one penny” to the National Republican Senatorial Committee (NRSC), of which Cornyn is chairman. The online group’s description says: “First they supported Chafee. Then they supported Specter. Now they support Crist.” Its organizer and “admin” is Erick Erickson of the popular conservative blog RedState.

This isn’t just a story of how cutting-edge technologies can cut both ways. Cornyn has found himself caught up in the struggle between conservatives and moderates over the Republican Party’s future. Several primaries in upcoming races will feature party-backed moderate candidates facing off against strong conservative challengers. The showdown brewing between Florida Gov. Charlie Crist and former state House Speaker Marco Rubio for Republican Mel Martinez’s U.S. Senate seat is just the latest front in this ongoing battle.

Cornyn’s decision to weigh in on behalf of Crist can be explained by a headline that appeared in the Hill in February: “Florida Senate poll shows Crist annihilating field.” The numbers haven’t changed much since then. A Mason-Dixon poll taken in May shows Crist leading Democratic Rep. Kendrick Meek 55 percent to 24 percent and Democratic state Sen. Dan Gelber 57 percent to 22 percent. Rep. Ron Klein, a Democrat who has twice won in a Republican-leaning district, is considered somewhat less likely to run. Crist last led him by 34 points. Rubio doesn’t fare much better than the Democrats. Mason-Dixon shows Crist clobbering him 53 percent to 18 percent, with 29 percent undecided.

But head-to-head matchups show Rubio would be competitive if he managed to make it to the general election. “Rubio could win but he’d need our help,” says a Senate Republican staffer. “Crist would be the overwhelming favorite and we wouldn’t have to lift a finger.” The idea is to keep the Florida Senate seat safe while Republicans—already a beleaguered minority—have to defend more ground than the Democrats.

Except that the GOP also needs to repair its image and offer a bold contrast. Many conservatives believe that a Senator Rubio would do that more effectively than a Senator Crist. “Rubio is everything older Republicans like Crist should be encouraging,” argued Dan McLaughlin on RedState. “He’s young but already experienced as a leader, he’s telegenic and a good speaker, he’s conservative, and yes, he’s Latino, a demographic that a more inclusive Republican party would be reaching out to, not spurning.”

The conservative Hispanic Leadership Fund had a similar reaction. “We are highly disappointed that the Republican establishment would slam the door on Marco Rubio, who is the kind of candidate that the GOP should be eagerly supporting,” read a statement from the group. “We have heard a lot of talk about how the party wants to find qualified Hispanic candidates to run for office but in the end we see once again that this is nothing but lip-service.”

Conservatives have gotten angry with the NRSC before. Despite the recent focus on the Club for Growth, the NRSC has intervened in competitive Republican primaries and helped rescue moderate-to-liberal incumbents from conservative challengers. The NRSC—along with then Sen. Rick Santorum and then President George W. Bush—came to the aid of Sen. Arlen Specter in Pennsylvania five years ago, helping him narrowly beat back a strong primary challenge from Pat Toomey. When it looked like they would be unable to defeat Toomey a second time, Specter switched parties and put the Democrats on a path to a 60-seat, filibuster-proof supermajority.

The NRSC also helped bail out Sen. Lincoln Chafee of Rhode Island, the most liberal Republican senator, when Cranston mayor Steve Laffey challenged him from the right in 2006. Chafee was not just pro-choice. He routinely voted against Republican positions almost across the board, with National Journal ranking him to the left not only of Specter but also of Democrats Mary Landrieu of Louisiana and Ben Nelson of Nebraska. In 2005, Chafee scored 12 out of 100 in the American Conservative Union’s rankings—the same as Hillary Clinton and a point worse than Russ Feingold.

Given this voting record, if Chafee had held on to his Senate seat—giving the GOP 50 senators in 2007–08 plus Vice President Dick Cheney’s tie-breaking vote—Republicans would not have had effective control of the chamber. They would have had to bargain with a liberal Northeastern senator to pass anything. And given what ended up happening with Specter this year and Vermont Sen. Jim Jeffords in 2001, Republicans might not have been able to maintain nominal control, either. Chafee ended up leaving the party after the 2006 election, even though he won both his primary and 94 percent of Republican votes in November.

But at least Chafee was an incumbent with some chance of winning, while Laffey was a near-certain loser. (The more conservative Republican Gov. Donald Carcieri was able to win reelection in Rhode Island that year, but he wasn’t asking to be sent to Washington to vote with George W. Bush.) In 2004, Toomey was a weaker general-election candidate than Specter but no sure pushover: he’d thrice been elected to the House in a swing district that voted for Bill Clinton and Al Gore.

Specter-Toomey is a good model for some of the primary fights Republicans will be facing this year: either the moderate or the conservative could win, but the moderate has stronger poll numbers right now. The first such race was decided in June. New Jersey Republicans faced a choice between moderate former U.S. attorney Chris Christie and conservative former Bogota mayor Steve Lonegan.

The incumbent Democrat, Gov. Jon Corzine, is very vulnerable and could conceivably be beaten by any credible Republican challenger. A May Quinnipiac poll showed Christie leading Corzine 45 percent to 38 percent while Lonegan bested the sitting governor 42 percent to 40 percent (within the margin of error, though Lonegan has led Christie by as many as eight points). A story in Philadelphia’s The Bulletin described the Republicans’ dilemma well. One side has “seen the governor’s weakness as an opportunity to elect a strong economic conservative” in an “eminently populist and union-heavy state.” But “the prospect of beating an incumbent Democrat draws many Republicans to the reputedly more electable Mr. Christie.”

Connecticut Republicans still have this question ahead of them. A Quinnipiac poll showed former Rep. Rob Simmons mopping the floor with Democratic Sen. Chris Dodd by 50 percent to 34 percent. But Simmons is a quintessential moderate Republican, with a 55 lifetime rating from the American Conservative Union. The same poll showed more conservative state Sen. Sam Caligiuri edging Dodd 41 percent to 37 percent. Should the GOP take what might be a once-in-a-lifetime chance to possibly elect a more reliable conservative in a typically Demo cratic state, even though it means a tougher race? Or should they nominate the candidate with the best current numbers, going for what could be an easy win? (If Dodd remains this weak, Connecticut Democrats may decide to take matters in their own hands during their primary.)

Then there is Pennsylvania again. The political climate so far looks tougher for Toomey than in 2004 and the Republican establishment, without any seats to spare this time, seems no more eager to have him as the nominee. But Specter has already cleared the primary field and flipped the Senate seat Democratic. Former Gov. Tom Ridge, another moderate Republican, has decided to take a pass on the race. Maybe Rep. Jim Gerlach will eventually decide to challenge Toomey from the left. Right now, the GOP’s only other option is Peg Luksik, a paleoconservative who is to Toomey’s right.

Overall, Republicans have to be happy that their candidate recruitment is going so well absent unmistakable signs that 2010 is going to be the GOP’s year. Whatever outside groups like the NRSC and the Club for Growth do, the ultimate decision-making power belongs to Republican primary voters. But the competition between moderates and conservatives within the party isn’t going away. If anything, it is intensifying.