MADISON, Wis. (AP) — Millions of dollars poured into Wisconsin starting Monday for the final week of the election, as jittery Democrats tried to push Russ Feingold over the finish line in the U.S. Senate race against Sen. Ron Johnson, one of the key races nationwide that could determine whether Republicans retain majority control.

Republican presidential nominee Donald Trump and Democrat Hillary Clinton’s running mate Tim Kaine were also both headed to Wisconsin on Tuesday, as numerous surrogates including House Speaker Paul Ryan, Chelsea Clinton and former Democratic Sen. Herb Kohl make closing arguments and urge backers to vote now or on Election Day.

Johnson has long been seen as one of the most vulnerable GOP Senate incumbents this election cycle. Democrats are trying to retake control of the Senate, and must pick up four or five seats to do so, depending on whether they retain control of the White House.

Television spending in Wisconsin’s Senate race ratcheted up on Monday, with a super PAC backing Johnson releasing a six-figure statewide ad that appeared to concede a Clinton victory. The ad by the Let America Work PAC, featuring a steaming pile of cow manure, argued that Johnson needed to win to provide a check on Feingold and Clinton.

That ad comes after the Senate Majority PAC on Friday announced a surprise late $2 million ad buy in Wisconsin to help put Feingold over the top against Johnson. The Republican incumbent’s campaign has long argued the race is tightening, and nervous Democrats were refocusing on the race where Feingold had long been ahead to insure there isn’t a late surprise.

Clinton’s campaign also launched its first Wisconsin television ads of the campaign on Monday in Milwaukee, Madison and Green Bay. Clinton’s Wisconsin campaign director Jake Hajdu said the ads, costing at least $100,000, were designed to help Feingold and other Democrats.

Feingold was expected to campaign with Kaine on Tuesday for at least one of his stops in Appleton and Madison.

Trump and his running mate, Indiana Gov. Mike Pence, were scheduled to hold an evening rally on Tuesday in Eau Claire. Polls have consistently shown them trailing Clinton in Wisconsin, allowing her to focus her time elsewhere. She has not campaigned in the state since the primary in April.

While Johnson has stood by his backing of Trump, he’s also kept his distance and not campaigned with him in the state.

Johnson will be getting some help from other Wisconsin Republicans — including Ryan and Gov. Scott Walker — when a GOP bus tour launches on Thursday.

Clinton’s absence from the state is noteworthy. If she does not make an appearance here before the election, it will be the first time since 1972 that one of the two major party candidates for president did not campaign in the state during the general election season, based on research by University of Wisconsin-Madison political science professor Barry Burden.

Wisconsin hasn’t voted for a Republican for president since 1984 and polls this year have consistently shown her ahead. Also, since early voting started in late September, Democratic counties have come in stronger than GOP ones. Voters do not register by political party in Wisconsin, so it’s difficult to draw too many conclusions from the numbers.

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