There is no stranger support for Israel among Americans than fundamentalist Christians who hope to see Armageddon occur, triggered in the Middle East. They hope that Israel and Iran will get things going soon and the result will be the second coming of Christ and "the Rapture" of Judgment Day when the quick are separated from the dead, they being among the saved and, as such, able to witness the tortures and destruction of the damned.
It's not a pretty picture and not the kind of thing that I think should stimulate people to write to their Congressman urging support of Israel. It is the exact opposite of rationality and a throw-back to the worst days of religious thought.
Nevertheless, these folks are active and vocal and represented by John Hagee of CUFI - Christians United for Israel. You really should listen to Hagee speak as it is with the kind of pomposity and certainty that could easily lead uninformed people to anything.
Who better to debunk him than Jews, who are in a position to negate his many authoritative statements about them. Ed Anser narrates a video doing just this.
For a very thorough look at CUFI, including an analysis of how it presents support for Israel in euphemisms, Jews on First (because if Jews don't speak out...they'll think we don't mind) has a complete report on the latest annual CUFI convention.