Student and gun control activist David Hogg has now turned his sights on one of the most high-profile U.S. senators in Congress: Sen. John McCain (R-AZ).

The 17-year-old tweeted Friday to McCain, who is in Arizona, recovering from brain cancer treatment, “Why do you take so much money from the NRA?”

Why do you take so much money from the NRA? — David Hogg (@davidhogg111) March 30, 2018

McCain has not responded to Hogg’s tweet.

The Arizona senator and chairman of the Senate Armed Services Committee is the top recipient of donations from the National Rifle Association, according to the Center for Responsive Politics.

According to the center, McCain has received $7.7 million from the NRA.

Hogg’s tweet comes after he called for his Twitter followers to pressure advertisers to pull their ads from Fox News show host Laura Ingraham’s broadcast, after she said he was whining about college rejections.

“David Hogg Rejected By Four Colleges To Which He Applied and whines about it. (Dinged by UCLA with a 4.1 GPA…totally predictable given acceptance rates.),” she tweeted.

David Hogg Rejected By Four Colleges To Which He Applied and whines about it. (Dinged by UCLA with a 4.1 GPA…totally predictable given acceptance rates.) https://t.co/wflA4hWHXY — Laura Ingraham (@IngrahamAngle) March 28, 2018

She later issued an apology, after advertisers being pulling their ads from her show.

Any student should be proud of a 4.2 GPA —incl. @DavidHogg111. On reflection, in the spirit of Holy Week, I apologize for any upset or hurt my tweet caused him or any of the brave victims of Parkland. For the record, I believe my show was the first to feature David…(1/2) — Laura Ingraham (@IngrahamAngle) March 29, 2018

McCain, 81, is a six-term senator, Vietnam War veteran, and former prisoner of war. He was one of four Republicans who supported a bipartisan bill on gun purchase background checks in 2013, which did not ultimately clear the Senate.