In the weeks before November's midterm elections, a quiet but telling exodus is taking shape: the Republican candidates who most need to win are choosing their own doorsteps over the party's grand stage in Dallas. With President Trump's approval at 39 percent and history favoring the opposition in midterm years, those running in the nation's closest races are making a sober calculation — that proximity to power can be a burden as much as a blessing. The convention proceeds, balloons and all, but the empty chairs of the most vulnerable candidates speak a language of their own.