In total, Democrats spent nearly $30 million on the airwaves in Iowa and New Hampshire in 2019, according to Advertising Analytics, an ad tracking firm.

Not a single candidate has run a negative ad on television targeting other Democrats.

The relatively placid ads of the 2020 Democratic campaign reflect the risk-averse primary contest, in which candidates have been loath to unleash any negativity on an opponent. Instead, they are channeling voters still unnerved by the 2016 election and so wholly concerned with defeating Donald Trump that any potential damage done during the Democratic primary could be viewed as unforgivable.

While Democratic voters in Iowa find negative advertising particularly off-putting, it appears that they want to both get rid of Mr. Trump and eradicate his confrontational approach to politics.