A Democratic outside group is canceling the first two weeks of its advertising in the Ohio Senate race, a sign that national Democrats are increasingly pessimistic about Gov. Ted Strickland’s campaign against Republican incumbent Sen. Rob Portman.

Senate Majority PAC, a super PAC with ties to Democratic Leader Harry Reid that is the party’s main outside spending group for Senate races, is delaying its initial fall advertising in the race, according to two ad buying sources who requested anonymity. The group was slated to begin fall advertising on Sept. 6, but is now delaying its reservations through Sept. 19.

The news comes the day after the Democratic Senatorial Campaign Committee delayed its advertising in the race from Sept. 13 until Sept. 22, according to The Washington Post, though the DSCC is still spending to help fund an ad run by Strickland’s campaign.

Senate Majority PAC has already spent $10 million on the Ohio Senate race both attacking Portman and backing Strickland, and had pledged $9.5 million in fall spending. Though the first two weeks of its advertising have been cancelled, the group has not yet changed the rest of its advertising slated to run in Ohio through Election Day.

“We regularly adjust strategy to maximize our resources and make sure we’re in the best possible position to win back the majority this November,” Shripal Shah, a spokesman for Senate Majority PAC, told RealClearPolitics in a statement.

The wave of advertising delays from Democrats is a sign that Ohio is looking increasingly difficult to flip in their favor this year. Portman has opened up a significant lead in the polls – he’s ahead by 7.5 percentage points in the RealClearPolitics average – and Strickland has not led in a public poll since May.

National Republicans have pointed to Portman’s campaign as the best example of GOP senators running ahead of their party’s presidential nominee in difficult swing states, praising the incumbent’s grassroots efforts and messaging. Donald Trump trails Hillary Clinton by nearly four points in the Buckeye State, but Portman, who has endorsed the party’s nominee, has avoided being dragged down by the top of the ticket.

Strickland and other Democrats point to more than $30 million in spending against him from Republican groups as the reason for his deficit in the polls, and in an interview with RCP last week, the former governor insisted the race is still close.

“I will admit right now I’m a little behind, but I’m not a dead dog because they’re still kicking me,” he said.

Ohio and national Democrats said they expect to see the race tighten in coming weeks as Strickland and outside groups expand their own spending on the contest, countering Portman’s messaging about Strickland’s tenure as governor. The cancelled ad buys from two top national Democratic groups, however, will complicate the party’s ability to keep pace on the airwaves in Ohio and will make it more difficult to cut into Portman’s lead in the polls.

Republicans have a four-seat majority in the Senate, but are defending 24 seats to Democrats’ 10. Nine races are labeled tossups by the Cook Political Report, including Ohio, and Democrats would have to take just four of those to win back the Senate if Clinton wins the White House.