A Democratic super PAC is upping the ante in the Iowa Senate race, underscoring that the contest has become a top target for Democrats looking to flip the chamber.

Senate Majority PAC is reserving an additional $3.6 million in television air time to launch ads starting in August, bolstering the Democratic nominee, real estate executive Theresa Greenfield, in her race against Republican incumbent Joni Ernst. The group already reserved $13.1 million in air time for the fall and its nonprofit arm Majority Forward has also been spending in the race.

“There’s a reason Iowa has become more competitive by the day. Theresa Greenfield has proven she’s the perfect foil for Joni Ernst and has made inroads statewide with her powerful story and commitment to protecting Social Security,” SMP spokeswoman Rachel Irwin said. “Poll after poll tells us what Iowans already know: Joni Ernst is vulnerable and has become another typical D.C. politician who can’t be trusted.”

Outside groups in both parties are planning to pour money into the Hawkeye State. Senate Leadership Fund, a GOP super PAC, has reserved $12.6 million in air time. The Democratic Senatorial Campaign Committee has reserved $7.3 million in TV and digital ads for the fall. The National Republican Senatorial Committee has already spent more than $2.7 million in Iowa.

Senate Majority PAC has also already spent $7 million in Iowa, largely before the June 2 primary in which Greenfield faced a handful of opponents.

The latest fundraising reports showed Ernst with a financial advantage in the race. As of May 13, her campaign had $7 million in the bank to $4.7 million for Greenfield, according to pre-primary reports filed with the Federal Election Commission. Fundraising reports for the second quarter, which ended June 30, are due next week.

Iowa is a top target for Democrats, who need a net gain of four seats to flip the Senate, or three seats if their presumptive nominee Joe Biden wins the White House since his vice president would cast a tie-breaking vote. President Donald Trump carried Iowa by 9 points in 2016, but Democrats, who hold three of the state’s four House seats, believe the state will be competitive in November.

Inside Elections with Nathan L. Gonzales rates the Iowa Senate race Lean Republican.