Welcome to Trail Guide, your daily run along the road to the White House. It's Friday, Aug. 21, and this is what we're watching:
- Donald Trump is set to hold a rally in a 40,000 seat college football stadium in Alabama - will he fill it?
- Jeb Bush, Ted Cruz and other Republican presidential hopefuls arrive in Ohio for a summit hosted by the conservative group Americans for Prosperity
- Martin O'Malley traversed through California Thursday, speaking to tech folks and young Democrats
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