Republican Sen. Dan S. Sullivan is in the middle of a competitive race as he seeks re-election this year in red-leaning Alaska in a midterm showdown that's one of roughly a dozen that will determine if the GOP keeps control of the Senate.Working against Sullivan as he runs for a third six-year term in the Senate is not only a rough political climate facing Republicans but also Alaska's unique electoral system, which includes four candidates from an open primary advancing to the general election and ranked-choice voting.Alaska is the only state in the nation to have a "top four" primary system...