FILE – In this June 23, 2016, file photo, Sen. Rob Portman, R-Ohio speaks on Capitol Hill in Washington. AP Photo/Alex Brandon, File

WASHINGTON — The difference between Senate Majority Leader Mitch McConnell staying in charge of the Senate or Democrats taking control may end up being one lackluster Democratic Senate candidate from Ohio who failed to realize the importance of the heroin epidemic.

Assuming Democrats win the White House, they need to flip just four Senate seats from Republicans to regain control of the upper chamber. And when the Senate races were starting to shape up last fall, Democrats saw Ohio as an excellent prospect for one of those, with former Gov. Ted Strickland challenging Republican Sen. Rob Portman.

But it’s not working out so well. Strickland is slipping in the polls, and Democratic campaign groups have begun to yank their spending from the race, moving to other states.

Democratic operatives who were willing to talk about the campaign on background said it came down to a few simple reasons, with the biggest being that Strickland has simply failed to raise the money needed to keep up in a state that has a dozen media markets. According to federal election reports tallied by the Center for Responsive Politics, as of June, Portman had out-raised Strickland $21 million to $7 million.

On top of that, Democratic insiders said, Portman has probably run the best GOP campaign this year, managing to distance himself from toxic Republican White House nominee Donald Trump while connecting better with Ohio voters than the former governor.

Dan Birdsong, who teaches politics at the University of Dayton, said that in a state like Ohio in a presidential year, Strickland should be doing better.

Both candidates started the contest with surprisingly low voter-recognition levels, Birdsong said, with some 20 percent of voters saying they didn’t know enough about the sitting senator or the ex-governor to choose one.

But it was Portman’s campaign that better seized the opportunity to define Strickland negatively with those voters, casting the 75-year-old as a “retread” and a failure for Ohio because Strickland happened to be in office during the recession. Portman also has been doing a better job improving his own image.

“You’re not seeing the same kind of voter engagement from the Strickland campaign, or even from the ads,” Birdsong said. “You’re not seeing the same kind of ads from the Strickland campaign that could have defined Portman earlier in the summer, when it needed to happen.”

It’s not that Team Strickland and his backers didn’t try, attempting to link Portman to Wall Street and China in ad campaigns. But the economic-based attacks don’t seem to have worked, perhaps because Ohio’s economy is doing relatively well right now.

What does seem to have boosted Portman is his aggressive push on the opioid epidemic. In the waning days of the Senate’s spring session, Portman pushed hard to get the Comprehensive Addiction And Recovery Act passed. Although Democrats noted repeatedly that Portman failed to get any money attached to that legislation, his campaign has touted his efforts exhaustively in positive advertisements.

“The heroin ads that Portman has done seem to have been a better issue to pull people to Portman than the Wall Street ads of the groups aligned with Strickland moved people away,” Birdsong said. “The Wall Street ad holds water with those who were going to support Strickland anyway, but they weren’t getting to the persuadable people.”

In an election year that has proved anything but predictable, Strickland certainly can’t be written off, even if many Democratic insiders have done so by shifting spending to other contests. And his campaign certainly wasn’t ready to turn off the lights and box up its headquarters.

“There’s still a lot of race left to run, and there’s no one who knows Ohio better or is a stronger grassroots campaigner than Ted Strickland,” said David Bergstein, a campaign spokesman.

“We just recently launched our paid media campaign, the national environment is rapidly deteriorating around Portman, he’s facing a daily firestorm about his continued support for Trump ― and Portman’s small, weak field operation can’t compete with the Ohio Democratic Party’s coordinated field campaign which has hundreds of organizers and volunteers across the state working to elect Ted, Secretary Clinton and Democrats at every level,” he added, noting that Strickland has an especially busy schedule over this Labor Day weekend.

“Ted’s going to do what he does best: campaign vigorously across Ohio, talking about the central contrast in this race,” Bernstein said.” “He’s fighting for working people because that’s where he comes from and that’s who he cares about, while Sen. Portman is looking out for his rich and powerful friends.”

Even without Ohio, many prognosticators say Democrats have a strong chance to win back the Senate. But if they fail, Ohio will be the one that got away.

Here are The Huffington Post Pollster averages for the Ohio Senate contest: