U.S. Sen. Tammy Baldwin has a 40 percent favorability rating heading into her 2018 re-election bid, according to a new poll released Wednesday.

That's up slightly from 37 percent in October 2016. Thirty-five percent of voters surveyed by the Marquette University Law School poll said they view Baldwin unfavorably, while 24 percent lacked an opinion.

The Democratic senator's favorability ratings are similar to those of Republican Sen. Ron Johnson, who was elected to a second term in November 2016. Thirty-nine percent of voters said they view Johnson favorably, down slightly from 41 percent in October 2016. Johnson is viewed unfavorably by 39 percent of voters, while 26 percent said they had no opinion.

Republican groups at the state and national level have made Baldwin a top target for 2018, especially after Wisconsin voters supported Johnson and President Donald Trump in November.

Baldwin, who defeated former Gov. Tommy Thompson in 2012, is serving her first term in the Senate after representing Wisconsin's 2nd Congressional District for seven terms.