Pew Research Center's Forum on Religion & Public Life report released on 1/2/13) shows just how ludicrous that claim is.
The incoming 113th Congress is overwhelmingly christian -- with 482 of the 533 members of Congress being christians, or about 90.43%. Only 51 members of Congress do not claim to be christians, or about 9.57%. It is hard to imagine any "war" on christianity succeeding when 9 out of 10 members of Congress are christians. This means there is a much higher percentage of christians in Congress than in the population as a whole.
It is obvious that the Congress does not reflect the religious make-up of the country (where there is less than 80% of the population claiming to be affiliated with any religion at all). Another Pew Research Center survey showed that currently slightly more than 20% of the population claim no religious affiliation at all, and a few more percentage points are made up of those belonging to religions other than christian. That means than christians make up a percentage of the U.S. population somewhere in the low seventies.
While all religions (other than christians) are underrepresented in the current Congress, there is one group that is represented far less than any other -- those without any religious affiliation at all (composed of atheists, agnostics, skeptics, and those who just don't care about religion). This group composes at least 20% of the American public, but has only 1 representative in Congress (or about 0.187%).
When you break down Congress into the parties, it becomes obvious that the Republican Party is far less representative of the population at large than the Democratic Party. About 99.65% of all the Republicans in Congress are christians. The one Republican who is not christian is Eric Cantor (who is jewish). The Democratic Party is a bit more representative of the population, with only about 80.39% being christians. About 19.61% of Democrats do not claim to be christians ( with 1 claiming no religious affiliation, 10 refusing to answer the question, and 39 claiming to be members of other religions).
Frankly, as someone who's religious view is represented by only one member of Congress, I'm getting sick and tired of the christian claim that they are somehow victims of an imaginary war on christianity. In a country where the huge majority of citizens claim to be christians, and where 9 out of 10 members of Congress (and the president) are christians, the idea of christian victimhood is ludicrous.