Donald Trump's campaign is spending an incredible amount of money on lawyers, raising the eyebrows of campaign watchdogs and suggesting that they are fighting legal battles behind the scenes.

In a 10-week span from mid-June to the end of August, Trump’s campaign spent $1.1 million on law firm Jones Day, nearly as much on legal services as the $1.15 million Mitt Romney’s campaign did over the course of his entire 2012 campaign.

For comparison, Hillary Clinton spent $525,000 on her main law firm, Perkins Coie, over that same 10-week period.

Trump has built a reputation for controversy, but they often require attorneys to navigate. Over the course of his campaign, the businessman has generated headlines about shady campaign-finance practices, the political use of his charity, and high-profile campaign staff departures.

“It does show the unique nature of his candidacy. From the way he has run his campaign to where he’s putting his money, it’s not what you normally see,” said Larry Noble, the general counsel of the Campaign Legal Center, a nonpartisan group focused on campaign-finance laws. “It suggests that something is going on that is unusual.”

Over the course of the presidential campaign, Trump’s campaign has spent $2.5 million at Jones Day, or 32 percent more than the Clinton campaign has spent on lawyers. During his second election campaign, President Obama spent approximately $3 million on legal fees through December 2012, a figure that Trump appears set to exceed if he continues to spend at the rate he was spending in July and August.

Trump’s rate of spending is very strange and suggests that something not currently known is happening within the campaign, campaign-finance experts told The Daily Beast.

“That’s an extraordinarily high number and suggests that the campaign is engaged in litigation and/or investigations on numerous fronts,” campaign-finance lawyer Brett Kappel told The Daily Beast.

Added Noble, “We don’t know of any big lawsuits that the campaign is involved in.”

The Trump campaign did not respond to questions about why it was spending so much money on legal consultants, but over the course of his campaign, Trump himself has been under fire for his use of the Trump Foundation for political purposes, which is against the law. This controversy could drive up legal costs if the campaign is turning to its lawyers for advice on how to respond to questions about Trump’s charity.

The New York Attorney General’s Office announced in September that it had begun an investigation into the Trump Foundation’s activities. The charity distributed a $25,000 political contribution to Florida Attorney General Pam Bondi right before her office decided that she would not join a lawsuit against Trump University, sparking allegations of a quid pro quo. The Trump Foundation has also been used as a vehicle to distribute funds to veterans charities at political rallies, which is also a violation of the rules.

But there are many other possible reasons. The campaign has parted ways with many senior staff: Campaign managers Corey Lewandowski and Paul Manafort, former Trump delegate manager Ed Brookover, and communications aide Michael Caputo have all left, just to name a few—any of their departures could have led to arbitration or litigation.

There was one case that led to legal action: In May, Trump sued former campaign aide Sam Nunberg, seeking $10 million in damages from Nunberg over an alleged breach of a nondisclosure agreement. This was later settled in August.

Trump’s campaign is unique also in that it likely required legal advice over the potential of a contested Republican convention. With many Republicans opposing Trump’s nomination, and a movement called Free the Delegates that sought to undermine the businessman’s support on the convention floor, Trump’s campaign may have needed advice from lawyers on how to navigate these obstacles.

“The legal costs could also be driven up by responding to Federal Election Commission complaints,” Kappel said.

The Republican nominee is also famously litigious, even while running for president: Just this past weekend, Trump threatened to sue The New York Times over an investigative report about his leaked 1995 income-tax returns. He also threatened to file a lawsuit against Sen. Ted Cruz for “not being a natural-born citizen,” and pledged to “open up” libel laws if elected president.

Trump has run also run a campaign that declines to follow traditional patterns of high spending on field operations and advertising, focusing instead on promoting the candidate at large rallies that whip up excitement among the GOP faithful.

But it’s this strategy that makes his high spending on lawyers all the more unusual. Presidential campaigns typically spend legal consulting money to provide legal advice to staff operating in the field—but Trump’s campaign doesn’t have a very robust ground operation, unlike conventional campaigns such as Mitt Romney’s 2012 run.

“Both Romney in 2012 and Clinton this year have ground operations in more than 30 states and spent heavily on advertising, both of which drive up legal compliance costs. Trump has an extremely limited ground operation and has done a historically small amount of advertising, so the legal fees must be due to something else,” Kappel said.

Trump has wielded a team of high-powered lawyers as a strategic tool his entire career. In many ways aggressive legal action has been key to his entire business strategy. This presidential campaign has done little to change his instincts.

And he’s got the lawyers’ bills to prove it.