"It looks like Trump is losing by a few % points; wouldn't be too good for his positioning to lose Iowa and I'm guessing if that holds, that -500+ bet against him winning the Presidency is going to go a lot higher."
It's at -1200 (that the field wins) now ..... and Trump is now a solid underdog to take the nomination itself, at +220, Vs. Rubio at -135. These numbers change quickly this far out. There's a school of thought that thinks the Republican establishment (or what is left of that) would rather have Trump be the nominee, as they could accept a "one and done" defeat of him Vs. Rubio, would could leverage the nomination into a larger power grab.
Trump is a solid favorite in New Hampshire though and him winning that would move the lines a lot, I guess.