Why? The D's as a group are outspending Trump, in fact the top 3 D's are outspending Trump. I'd be interested to see this type of analysis for the 2016 (and 2012 and 2008) elections.
Well it surprises me because Trump already has the nomination and it's not even time for the general election yet, the D's are essentially running right now, Trump is preparing to run.
Edit: actually looking at his ads, they're asking for fundraising so that makes sense if he's getting positive ROI.
Edit: actually looking at his ads, they're asking for fundraising so that makes sense if he's getting positive ROI.