Conservatives have already spent millions against Tammy Baldwin
Conservative groups have already spent approximately $3.1 million on attacks ads attack Wisconsin's Democratic senator Tammy Baldwin, per HuffPost. They've spent another $1.6 million boosting her Republican opponents.
Why it matters: There are 10 Democratic senators up for re-election this year in states that Trump won. But if conservative groups spending is any indication, Wisconsin might be the hardest seat for Democrats to keep — and that should have the party worried at every level because Sen. Baldwin is one of two Democrats serving statewide in Wisconsin.