Speaking to a group of students at the University of Louisville on Sunday, Sen. Elizabeth WarrenElizabeth Ann WarrenWarren: Trump is a 'racist bully' Poll: Oprah would outperform Warren, Harris against Trump in California Democrats continue to dismiss positive impacts of tax reform MORE (D-Mass.) said incumbent Senate Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellSessions: 'We should be like Canada' in how we take in immigrants NSA spying program overcomes key Senate hurdle Overnight Finance: Lawmakers see shutdown odds rising | Trump calls for looser rules for bank loans | Consumer bureau moves to revise payday lending rule | Trump warns China on trade deficit MORE (R-Ky.) is more interested in protecting "billionaires" than students.

"When you've got a choice between billionaires and students, Mitch McConnell says it is more important to protect the billionaires," said Warren, according to The Associated Press. Warren was in town raising support for Kentucky Secretary of State Alison Lundergan Grimes, a Democrat who is challenging McConnell in the November elections. "And that's what this race is all about. It's about a man who stood up and filibustered the student loan bill," Warren said.

As the GOP looks to take back control of the Senate, the upper chamber's most important Republican is locked in a tight race with Grimes. Hoping to give her campaign a boost, Warren traveled to Kentucky this weekend to raise support for Grimes.

They spoke to hundreds of Louisville students about college affordability. Warren pointed out that McConnell blocked a bill she introduced to lower student loan interest rates, because it would raise taxes on the wealthy.

Grimes said education "should be the passport out of poverty, not into poverty," at the rally.

Grimes has focused much of her attention on issues such as raising the minimum wage, ensuring equal pay for women and, most recently, making college more affordable for students.

But Grimes also has strong ties to the Obama administration, which doesn't play well in Kentucky, critics say.

Following the speech, Grimes and Warren attended a nearby fundraiser in Kentucky.