More importantly it has hurt Christianity:

Republican senator scheduled to speak at next year’s New Baptist Covenant Celebration in Atlanta told a community newspaper in Iowa that positioning the party as the “Christian” choice has been detrimental to the GOP.
“That does turn some people off,” Sen. Chuck Grassley, R-Iowa, said in an interview with the Sioux County Index-Reporter. Grassley said he prefers to describe the party in a different way.
“I believe in the big-tent approach,” he said. “We ought to be open to anybody who shares our conservative economic, political and social views.”
Asked if ethical scandals like Idaho Sen. Larry Craig’s arrest for disorderly conduct in an airport men’s room diminish the GOP’s “Christian” identity, Grassley sought to distinguish between the two.
“I believe that a person can vote for whatever reason he wants to, and I think that on certain issues, it’s better to vote the Republican Party,” he said. “But I believe that you can make those arguments without using the religious point of view.”

Republicans should stop using Christians to get elected and Christians should refuse to be used. Christians have become yoked in the eyes of society with men and women who might not share the same beliefs and goals. It makes no sense for Christianity to become associated with one political party because Christ didn’t come to transform society though government but through changed lives lived for his glory. The goal of Christianity isn’t to become one more lobbying group trying to get our agenda passed, our goal is to spread the gospel to a lost and dying world.
Yeah, I know that this isn’t a popular position among Christians and conservatives.
BTW, I’m not saying that Christians shouldn’t be involved in politics, I’m saying that the name of Christs shouldn’t be used to get someone elected.
And then there’s this from the same article:

Grassley is one of two sitting U.S. senators scheduled to speak at the Jan. 30-Feb. 1 New Baptist Covenant Celebration at the Georgia World Congress Center. The other is Sen. Lindsay Graham, R-S.C.
The meeting was announced in January at a press conference featuring former presidents Jimmy Carter and Bill Clinton, flanked by representatives of more than 30 Baptist organizations involved in planning. Clinton and Carter are also scheduled speakers for the celebration.
A third high-profile Republican, presidential candidate Mike Huckabee, withdrew from his invitation to speak at the gathering to protest comments attributed to Carter that were critical of President Bush. The former Arkansas governor said he had only “tentatively” agreed to participate in the convocation with the understanding it wasn’t political. In pulling out of the commitment Huckabee said the program “does seem to tilt left.”

Even if it “tilts left,” why not go and present your vision for the future? Why not make your case and let the best argument win? It seems very short-sighted to me.
There is also the news making aspect of it if he were bold enough to give a speech about Carter’s failure as a president and how we are still suffering the effects of those failures (Iran).