1:20 p.m.: UPDATED with a response from McCaskill.
A Koch brothers-funded ad blitz against U.S. Sen. Claire McCaskill starts this week, with $1.8 million worth of television and video spots going after the Missouri Democrat for her opposition to the recent Republican tax overhaul.
"Tax reform is sweeping across Missouri. Small businesses are growing. Pay checks are going up," says a female narrator in one of the spots, over an image of the Gateway Arch and a montage of regular people working and playing.
"Senator Claire McCaskill said she'd support tax cuts for hardworking Missourians, but when she had the chance, she said `no,' " the narration continues.
It gets in a dig about her "standing with Chuck Schumer and Nancy Pelosi," showing a sinister-looking black-and-white image of the two Democratic leaders. The narration closes with, "Tell Sen. McCaskill to put Missouri jobs first."
At issue, of course, is the package of federal income tax cuts and deduction changes that Republicans pushed into law late last year.
McCaskill, running for a third term this year and leaning on her long-cultivated position as a political centrist, did express support for the concept of tax cuts during last year's tax debate. But she ended up joining all her fellow Senate Democrats in voting against the bill, arguing that most of the benefits were top-loaded to the wealthiest Americans and that the plan would saddle the nation with massive new levels of debt.
McCaskill on Tuesday blamed Senate Republican leader Mitch McConnell of Kentucky for shutting off debate and potential Democratic support on the tax bill and on the GOP's attempts to repeal and replace Obamacare in 2017. McCaskill said she had continuously expressed a willingness to work with Republicans in both areas, but that the GOP had embarked on a strategy early in 2017 to go ahead with Republican support only and then attack Democrats who voted against them.
"I said over and over again in every way I could, 'I want to work, there is a tax bill I can support, there are healthcare reforms I can support. Talk to us, let's find middle ground,' " McCaskill said. "They did not want to do that. So using the last year as a mark against bipartisanship lies solely at the feet of Mitch McConnell."
McCaskill's campaign also responded to the ad blitz Tuesday with a detailed "fact check" webpage laying out her attempts to negotiate a compromise tax reform plan with the Trump administration, and noting that the Koch brothers "have personally benefitted from the Republican tax bill" by as much as $1 billion annually by one estimate.
McCaskill is one of the national Republicans' top Senate targets this year, as she tries to win over voters in a state that has been getting more conservative during her Senate tenure and which overwhelmingly supported Donald Trump in the 2016 presidential election.
The independent campaign against McCaskill and Sen. Joe Donnelly, D-Ind., who is in a similar political situation, is funded by Americans for Prosperity, which is backed by billionaire conservative activists Charles and David Koch.
The anti-McCaskill ad, part of a blitz that officially begins Thursday, can be viewed HERE.
—Chuck Raasch of the Post-Dispatch staff contributed to this report.