CHICAGO -- Television executives worried about potential lost revenue if Donald Trump doesn't advertise as much as past presidential candidates can take solace in this: There are likely to be at least a half dozen competitive U.S. Senate races in mostly big states where it's expensive to buy airtime.

While the billionaire and former reality television star proved it's possible to become a presumptive presidential nominee without spending much on advertising, most of those running for Senate won't have the luxury of following his example.

More than 86,000 broadcast television spots have already run this year as part of Senate races, at an estimated cost of $83 million, according to a Bloomberg Politics analysis of data from ad-tracking firm Kantar Media/CMAG.

As the campaign moves into the general election phase, the potential exists for higher spending than normal, especially if establishment Republican donors direct resources to state races instead of the White House campaign. The GOP is trying to maintain control of the Senate and the House, while Democrats sense an opportunity.

"Trump at the top of the ticket may lead to even greater spending in down-ballot races as certain states become more competitive and groups that were planning on spending in the presidential contest redirect resources," said Ken Goldstein, a University of San Francisco professor who is a Bloomberg Politics polling and advertising analyst.

Sinclair Broadcast Group Inc., Tribune Media Co. and Nexstar Broadcasting Group Inc., among the largest owners of broadcast TV stations in the U.S., could benefit from increased political advertising.

The political network backed by billionaire industrialists Charles and David Koch plans to spend more than $42 million on ads in key Senate races between now and September, the Washington Post reported this week. That spending will include $2.2 million for television and digital ads in Ohio targeting former Democratic Gov. Ted Strickland, who is challenging Republican incumbent Sen. Rob Portman.

"In states like Ohio, where the Senate race always figured to be in play, the unpredictable effects of Trump at the top of the ticket and confusion about the campaign efforts that he will pursue may make advertising even more important for an incumbent like Rob Portman, who may not be able to count on normal levels of Republican turnout or loyalty in the Buckeye State," Goldstein said.

So far, Portman and Strickland haven't run their own ads on broadcast television. That will soon change. Portman's campaign last week announced a $15 million advertising effort that will run through November's election, with $14 million budgeted for statewide television and $1 million for YouTube through Google's advertising network.

Outside groups have already been busy trying to influence the race in Ohio, a perennial battleground state in the presidential race. The Democratic Senate Majority PAC has been the top Senate-race advertiser so far this year in Ohio, airing almost 1,900 spots on broadcast television at an estimated cost of $3 million. All of the group's ads have been negative in tone, according to the Kantar Media/CMAG data.

While some television executives have worried that Trump's tendency to advertise less than most presidential candidates could hurt their bottom lines, others remain optimistic.

"We expect to generate the vast majority of our political ad revenue not from the presidential campaigns, but from the Senate races, gubernatorial races, political action committees and cause-based advertising," Peter Liguori, the chief executive officer of Tribune Media, told investors on an earnings conference call last week.

Tribune, which owns or operates 42 local TV stations and the WGN America cable network, generated "about $166 million in gross political advertising in 2012," Liguori said, with the company projecting that number to grow to $200 million this year. "While it's early, we're off to an incredibly good start," he told investors, adding that political ad revenues in the first quarter were up 169 percent compared to four years ago.

Among Senate candidates facing serious general election races, the Bloomberg Politics analysis found Pennsylvania Democrat Katie McGinty has been the top advertiser so far in 2016. The former chief of staff to Gov. Tom Wolf is challenging Sen. Pat Toomey in a state that's likely also to be hotly contested in the presidential campaign.

McGinty has run more than 5,100 spots so far this year, with many of those airing ahead of her victory in Pennsylvania's April 26 primary.

Toomey has run more than 3,000 spots this year, with 85 percent of them being positive in tone. That trend changed during the first week of May -- once his general election rival was known -- and they've all been negative since.

Pennsylvania is easily the top state for Senate-related ads so far this year, with 19,771 run on broadcast television through May 16.

In dollar terms, a super PAC run by the Democratic women's group Emily's List has been the top spender so far this year among those trying to influence Senate races.

Women Vote has already spent an estimated $6.6 million, broadcasting more than 4,200 spots so far. The group has spent in only two states this year: Pennsylvania to boost McGinty and Maryland to help Donna Edwards, who lost an April 26 primary to Rep. Chris Van Hollen.

Broadcasters especially like super PAC business from groups like Women Vote because the outside groups often pay some of the highest rates. That's because they often place ads at the last minute, when rates are higher, and they're not guaranteed the lowest rate available, as required by law for actual candidates.

Those factors mean that super PACs and other outside groups making late buys can pay four or five times as much as candidates for the exact same ad inventory. In other words, a few super PAC buys made late in Senate races could make up for a lot of early candidate orders not made in the presidential race.

After Women Vote, Sen. Richard Shelby of Alabama is the next biggest Senate race spender on broadcast advertising so far this year. His campaign spent an estimated $5.2 million ahead of a March primary to avoid having a runoff with a challenger.

Shelby, who is chairman of the Banking, Housing and Urban Affairs Committee and doesn't face a serious general election challenge in a state that leans heavily Republican, is certain to quickly be eclipsed in spending as the general election season moves into high gear.

With some of this year's most heated Senate races playing out in states where it's more expensive to advertise, total dollar amounts spent are likely to soon spike higher.

The race in Illinois between Republican Sen. Mark Kirk and Democratic Rep. Tammy Duckworth is likely to be one of the most expensive in the nation because it involves a large state and includes the expensive Chicago media market. Kirk has already spent more than $500,000, the Kantar Media/CMAG data shows, while Duckworth has spent more than $916,000 for her primary campaign and for the start of her general election bid.

Florida, where there is an Aug. 30 primary to fill the seat being vacated by Republican Sen. Marco Rubio, will also host one of the most expensive Senate races this year.