Sean O'Brien, the big boss of the Teamsters union, is helping Roger Marshall win. Marshall is a Republican who wants to be a senator.
Mr. O'Brien likes Mr. Marshall because he thinks Marshall will make laws that help workers. Even though he's from the Republicans' side, sometimes he votes like a Democrat does for worker rights.
Marshall's main opponent is Adam Hamilton. He's a Democrat and also a pastor. Kansas usually picks Republican candidates in big elections, so Marshall needs extra support to win this time.
The Teamsters Local 696 group also thinks Marshall will help workers, so they are backing him too.
O'Brien has been getting closer to the Republicans since Donald Trump became president.
Marshall wrote laws like Josh Hawley's Faster Labor Contracts Act and led the Overtime Wages Relief Act. This act means people can keep more of their overtime pay by not taxing it as much.
Hamilton got almost $4 million for his campaign, but he still has a hard race in Kansas against Marshall.
Kansas hasn't chosen a Democrat to be a senator for close to 90 years now. So this election is very important.