Republicans running for President will debate again this week...as Ben Carson now leads an upset Donald Trump in Iowa.

FOX News Radio's Rachel Sutherland reports from Washington:

Two recent polls show Carson ahead of Trump in the bellwether state of Iowa... While a new CBS News "Battleground Tracker" shows them in a dead heat. Trump going on the offensive, telling CNN:

(Trump) "Ben Carson is lower energy than Jeb if you want to know the truth."

Carson responded on NBC's "Meet the Press"... saying he's not going to get into the mud pit of political sniping:

(Carson) "You know I am soft-spoken. I do have tendency to be relaxed."

Both candidates are gearing up for another Republican Presidential debate two days from now in Colorado.

In Washington, Rachel Sutherland, FOX News Radio.