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.

Freedom Partners' campaign will include 2 ads ("$5 Trillion" and "Absolutely Wrong") both focusing on how Baldwin's tax policies hurt Wisconsin residents and business owners.

What they’re saying: “The dishonest smear attacks continue as out-of-state special interests pour in millions of dollars to take down Tammy Baldwin and replace her with someone willing to sell out Wisconsin families,” said Brad Bainum, Democratic Party of Wisconsin spokesperson for the 2018 Senate race. “The truth is, Tammy supports tax cuts for Wisconsin working families."

Go deeper: Trump's admin wasn't always talking to Red-state Dems about taxes. And more on his tax plan.