The fight over Claire McCaskill's U.S. Senate seat is already one of the most-anticipated races of the 2018 midterms, and, so far, her Republican opponents are stumbling out of the gates.When it comes to money, McCaskill (D-Missouri) is rolling in it, to the tune of $11.8 million, according to her most recent campaign filings. Meanwhile, Missouri Attorney General Josh Hawley, presumed to be McCaskill's most potent Republican challenger, is holding just $1.2 million.…