SAN FRANCISCO: Advertising expenditure devoted to the US presidential election since the end of April is 60% less than over the same period in 2012, a leading political analyst has revealed.

Ken Goldstein, a polling and advertising analyst at Bloomberg as well as a politics professor at the University of San Francisco, said $146m had been spent since late April compared with $373m in 2012.

Although the campaign team for Donald Trump, the Republican presidential candidate, is expected to soon spend more with their first TV ads, Goldstein explained that they had concentrated until now on getting their message across through media interviews and Twitter.

In addition, spending by Republican outside groups, such as political action committees, has been less than in 2012, while spending was further held down by a Democratic primary season that lasted longer than four years ago.

"It delayed the start of general election advertising in battleground states where the real money is," Goldstein said.

Spending is expected to increase now that both parties have nominated their candidates, but Goldstein warned that, for local TV broadcasters such as Tribune Media, it won't make up for the four months of lost revenue.

However, Steve Lanzano, president of the Television Bureau of Advertising, struck a more optimistic note as he expected political advertising to increase for the Senate races.

"Certainly it's not what was expected," he said. "But you're going to see the money coming in. It'll just come in later."

Professor Goldstein also examined the Clinton campaign's broadcast TV adspend since mid-June and revealed it has spent around $50m so far. Some $13.3m was spent in Florida while another $10m was spent in Ohio, another key battleground state. Significant sums have also been allocated to eight other states.

Data sourced from Bloomberg; additional content by Warc staff