Republican U.S. Sen. Ron Johnson, left, and Democrat Russ Feingold, right, meet in their second and final debate Tuesday, Oct. 18, 2016 in Milwaukee, Wis. (Mark Hoffman/Milwaukee Journal-Sentinel via AP)

For months, Democrats have pursued the Senate majority quietly confident they had a strong advantage in at least two of states they need to win: Illinois and Wisconsin.

Both are reliably blue states in presidential years, and in Wisconsin, Democrats had the combination of a relatively unknown GOP incumbent in Ron Johnson and a well-known challenger in former Sen. Russ Feingold.

In polls taken through the summer, Feingold held a healthy lead over Johnson — double digits in some cases — as he was able to leverage his fundraising advantage to air positive ads early in the race.

Now, however, the race is looking like more of a squeaker. A poll released Wednesday by the Marquette University Law School shows Feingold up only a point over Johnson — 45 percent to 44 percent, with a three-point margin of error.

Other polls published in the past two weeks show Feingold with larger leads, ranging from five to 12 points, but the Marquette Law Poll holds a special hallowed status among Badger State political watchers, and the new result comes just as Democrats and Republicans alike have pumped new money into a race that seemed to be all but off the national board in September.

The tighter margins follow an October uptick in spending by Johnson and his allies, including a series of positive spots — such as one featuring him changing a diaper — that have helped increase his favorability among Wisconsin voters. Only 36 percent of likely voters had a positive impression of Johnson in early July, according to the Marquette Law Poll; that is now up to 43 percent.

“In an environment filled with cookie cutter political ads and a presidential campaign that is increasingly negative and devoid of substance, our creative ads have cut through the clutter,” Johnson campaign manager Betsy Ankney said in a memo last week.

National strategists for both parties acknowledge that the race has tightened, and Super PACs allied with both Republican and Democratic leaders have pumped millions into the final weeks of the race. Johnson has also benefited from spending from outside groups such as the Americans for Prosperity arm of the Koch political network.

What should be concerning to Feingold is that the latest spate of polls show Johnson performing more like his GOP Senate incumbent peers — that is, outperforming the top of his ticket by an appreciable margin — and starting to build an advantage among independents. But the Marquette Law Poll showed Democrat Hillary Clinton with a healthy six-point lead over GOP nominee Donald Trump, and the four-term former senator still has narrow advantages over Johnson in favorability and whether voters feel that he cares about their problems.

After months of trying to keep his distance from Trump, Johnson on Tuesday appeared at a Trump rally in an apparent bid to win the backing of pro-Trump voters.

Feingold spokesman Michael Tyler said his candidate “has the clear advantage heading toward Election Day.”

“While Sen. Johnson spends the last days of this campaign lashing out with child-like insults, clinging to Donald Trump, and failing to explain his years in Washington rigging the system for multi-millionaires like himself, Russ will close out this campaign the way he started it — listening to the middle class and working families of this state who want an economy that works for everyone, not just corporate CEOs,” he said.