A non-partisan, non-profit group launched a $1.6 million ad campaign today targets Wisconsin Sen. Tammy Baldwin's record on tax reform and urges residents to vote against her in 2018. The Freedom Partners Chamber of Commerce argues that Sen. Baldwin has "supported a long history of higher taxes."

Why it matters: This ad shows how the tax reform fight can become a political liability for some senators. Baldwin is one of 10 Dem senators representing states that Trump won in 2016 and whose seat is crucial for the Democratic Party to keep in 2018. Tax reform will be a difficult issue for the Red-state Dems whose constituents align more with the GOP and are likely to support Trump's tax plan — ultimately wanting their senators to do the same.