A prophecy by Joseph Smith, the founder of Mormonism. It is called the White Horse prophecy that states an ‘elder of zion’ (Mormon) will save the constitution when it is hanging by a thread.
I have heard non-Mormon Mittbots echo this sentiment as well.
It was originally given when Joseph Smith was running for POTUS in 1844, but has sense been thought of as a future event.
Here are a few sources (there are many many more and even a copy of it in the LDS owned museum there it was given - Liberty jail) and it is mentioned often in the official speeches of Mormon leadership and Rammell in ID caused a fuss by only inviting Mormon men (elders) to a meeting to discuss it during his campaign. There are also several FR threads that cover it.
http://www.ils.unc.edu/~unsworth/mormon/whitehorse.html
http://www.mormonwiki.org/White_Horse_prophecy
http://www.mrm.org/white-horse-prophecy
You will see the constitution of the United States almost destroyed. It will hang like a thread.... A terrible revolution will take place in the land of America.... [T]he land will be left without a Supreme Government,... [Mormonism] will have gathered strength, sending out Elders to gather the honest in heart... to stand by the Constitution of the United States.... In these days... God will set up a Kingdom, never to be thrown down.... [T]he whole of America will be made the Zion of God.
- Prophet Joseph Smith, Jr., May 6, 1843,
I had a feeling it had to do with Mormonism. The good thing the LDSers would vote for Romney anyway as one of their own so does not matter.
sense = since