WASHINGTON, D.C. — Sen. Sherrod Brown, D-Ohio, maintained a fundraising advantage over Republican opponent Bernie Moreno in the Ohio Senate race according to campaign finance reports filed Monday, in an election that could shift the balance of power in the Senate.

Brown ended the first quarter of the year with $16 million cash on hand, while Moreno had $1.8 million cash on hand.

The difference derives partially from a tight three-way GOP primary in March that sucked up resources from Moreno’s campaign.

“Absolutely you want to be the incumbent and you don’t want a battle in the primary because you don’t want to have to spend your money defeating other Republicans,” said Todd Belt, professor at George Washington University and director of its Political Management Program.

Brown raised $12.1 million from January through March, which according to his campaign is an Ohio record.

Moreno raised $3.8 million in the same time, including $1.5 million he personally loaned to his campaign. Of his loans, $1.2 million were made before the March 19 primary.

The Ohio race mirrors a broader trend across the country. In all four states the Cook Political Report lists as “toss up” Senate races—Arizona, Nevada, Montana and Ohio—Democrats reported more cash on hand than Republicans.

The Democratic Senatorial Campaign Committee (DSCC) spokesperson Tommy Garcia wrote in a statement,

“Battle tested Senate Democrats’ strong fundraising is a testament to the support they have earned from voters and grassroots supporters. While each day brings new revelations about Republican Senate candidates’ lies, baggage and disqualifying flaws, Senate Democrats are building winning campaigns and communicating with voters about how they are fighting for the priorities of hard-working Americans.”

The National Republican Senatorial Committee (NRSC) could not be reached for comment.

More funds are an advantage for Democrats heading into their general elections, but higher spending also reflects Democratic concerns that those seats could flip Republican.

“Democrats have so many more seats to defend this time around, particularly four are in states that were won by or very close to having been won by Donald Trump,” Belt said.

In Ohio, campaign spending will be divided between 12 different media markets. Though expensive, the large number of markets could help candidates.

“You can structure your advertisements to target your communities to a much greater and granular degree,” said Belt.

About $142 million worth of political ads have already been booked, according to AdImpact.

“I anticipate that we’re going to have $100 million thrown into this race by candidates and well over $100 million to be spent by outside groups to try to influence this election,” Belt said. “So what we’ve seen so far is just a drop in the bucket.”