NEW YORK (AP) — The Koch brothers are spending millions to attack two vulnerable Democrats for voting against the Republican tax overhaul.

The Koch-backed group Americans For Prosperity plan to launch a $4 million advertising campaign against Missouri’s Sen. Claire McCaskill and Indiana’s Sen. Joe Donnelly. An AFP spokesman said Tuesday the ad campaign will run on TV and the internet for three weeks beginning Thursday.

The ads accuse the senators of “voting against tax cuts for you” and “standing with” Democratic Senate leader Chuck Schumer and Democratic House leader Nancy Pelosi “instead of us.”

McCaskill and Donnelly are among several Democratic incumbents up for re-election this fall in states carried by President Donald Trump. Like all Senate Democrats, they voted against the tax overhaul because it gave preferential treatment to the rich.