Clinton outspending Trump $23 million to $0 in key states

For years, political scientists -- and some political operatives -- have wondered how much difference political advertising really makes in a campaign.

Measuring the effect is hard because, typically, both sides advertise, and one campaign's work tends to cancel out the other.

But Donald Trump seems set to run a real-time experiment in what happens when one side has a monopoly on the airwaves.

The Clinton campaign and its allies are airing just over $23 million in television ads in eight potential battleground states: Nevada, Colorado, Iowa, Ohio, Florida, North Carolina, Virginia and New Hampshire, according to data released by NBC News.

The Trump campaign? Zero.

Trump didn't advertise much in the primaries, and he has expressed skepticism about whether expensive television campaigns are worth what politicians pay for them.

The bigger problem, however, is that Trump's campaign lacks the money to respond to Clinton's ads. Although Trump has often claimed to be "self funding" his campaign, he hasn't been willing to fund very much, and it's unclear how much actual cash he has access to.

Many of the party's big donors, whom Trump attacked during the primaries, have shown little desire to bail him out. Some Republican mega-donors, including Sheldon Adelson, the Las Vegas casino operator, have said they will give money. Others, including the Koch brothers, have said they will not.

So, at least for now, the Clinton ads -- mostly biographical spots designed to improve her image with voters -- will remain unchallenged. And political scientists will get a real-world experiment they never expected: a gift from Donald Trump.