Ron Paul, who doesn't even return to the campaign trail until Wednesday, is already facing a barrage of attacks from his GOP rivals.

Newt Gingrich told CNN's Wolf Blitzer that he could not support Paul if he won the Republican nomination, adding his "views are totally outside the mainstream of virtually every decent American."

"I think the choice of Ron Paul or Barack Obama would be a very bad choice for America," said Gingrich.

Rick Santorum warned voters to carefully study Paul's record calling him "left of Barack Obama on national security."

Santorum added, "he can shut down our bases in Germany, he can shut down the bases in Japan. He can pull our fleets back. You think the rest of the world is going to say, 'Oh, that's great?' "

Santorum also challenged the crowd to study Paul's success as US Congressman adding "he's been in Congress for 20 years and hasn't passed a bill."

Michele Bachmann, in an appeal to social conservatives, said during a stop in Council Bluffs that "Ron Paul doesn't believe the government should protect the institution of marriage."

Paul is facing many questions concerning a decade's worth of incendiary newsletters which were published by the Texas Congressman and were written under his name. The newsletters contained bigotry against black, Jews, and gays and an obsession with conspiracies.

Although Paul said that he didn't write them, and has disavowed them, Gingrich said on CNN that the newsletters raised "fundamental questions" about Paul as president.

Paul is back on the campaign trail in Iowa on Wednesday with a Town Hall event in the afternoon and a salute to veterans rally later in the day.