Democrats are quietly fretting over Sen. Tammy Baldwin's Wisconsin senate seat, which could become a top priority for both political parties leading up to the 2018 elections, according to a report.

The Huffington Post reports that Democrats are increasingly worried about Baldwin's seat in a state that saw President Donald Trump defeat two-time failed presidential candidate Hillary Clinton—who did not once step foot in Wisconsin during the campaign—by less than one percentage point. Sen. Ron Johnson, an underdog months before the election, ended up pulling off a four-point victory over former Democratic Sen. Russ Feingold and ultimately garnered more votes than Trump in the state.

Republican groups have had their sights set on Baldwin, who was first elected to the Senate in 2012, and who is now the only statewide Democrat in Wisconsin, since last year.

Outside groups have already pushed $3 million dollars in outside spending into the state, where they have allotted more money than any other competitive race this election cycle to date. Democratic groups have pushed slightly more than $1 million in support of Baldwin into the state.

However, Baldwin has built up a massive war chest in regards to campaign funds. As of September of last year, Baldwin reported nearly $11 million dollars in receipts, with $9 million of that coming from individual contributions, according to filings. The remaining funds have come from political action committees.

Republicans Kevin Nicholson and Leah Vukmir, who are currently challenging each other in the primary, have respectively raised $417,000 and $242,000, their latest filings show.