FILE - In this Aug. 25, 2009 file photo, Sen. John McCain, R-Ariz., holds a healthcare town hall meeting in Sun City, Ariz. McCain's family says the Arizona senator has chosen to discontinue medical treatment for brain cancer. (AP Photo/Matt York)

FILE - In this Aug. 8, 2018 photo, Wesley Bell stands outside the Ferguson, Mo., police headquarters a day after he defeated longtime St. Louis County prosecutor Bob McCulloch in the Democratic primary. Bell's 57 percent to 43 percent victory over McCulloch, a white prosecutor first elected in 1990, is the latest win for the Black Lives Matter movement, which has increasingly shifted from protest to local politics in recent years. Voters concerned with the killing of unarmed black people by police have made their voices heard from Ferguson to Cleveland to Chicago. (AP Photo/Jim Salter, File)

President Donald Trump speaks to the media regarding the announcement that Supreme Court Associate Justice Anthony M. Kennedy is retiring, during his meeting with Portuguese President Marcelo Rebelo de Sousa in the Oval Office of the White House in Washington, Wednesday, June 27, 2018. (AP Photo/Pablo Martinez Monsivais)

As his wife Monica, left, looks on, Oklahoma Lt. Gov. Todd Lamb gives a concession speech in the Republican primary for Governor, in Oklahoma City, Tuesday, June 26, 2018. (AP Photo/Sue Ogrocki)

FILE - In this March 3, 2018, file photo, Mitt Romney speaks with a group during a breakfast campaign stop in Green River, Utah. Romney's annual gathering of top Republicans, wealthy political donors and powerful business leaders kicks off Thursday, June 7 in the Utah ski town of Park City with U.S. House Speaker Paul Ryan among the expected attendees at a three-day event that comes just weeks ahead of Romney's primary election in his bid to win the U.S. Senate seat in Utah. (AP Photo/Rick Bowmer, File)

FILE - In this March 3, 2018, file photo, Mitt Romney speaks with a group during a breakfast campaign stop in Green River, Utah. Romney's annual gathering of top Republicans, wealthy political donors and powerful business leaders kicks off Thursday, June 7 in the Utah ski town of Park City with U.S. House Speaker Paul Ryan among the expected attendees at a three-day event that comes just weeks ahead of Romney's primary election in his bid to win the U.S. Senate seat in Utah. (AP Photo/Rick Bowmer, File)

FILE - In this Nov. 25, 2013 file photo, President Barack Obama and Sen. Dianne Feinstein, D-Calif., greet each other on the tarmac upon his arrival on Air Force One at San Francisco International Airport. Obama is backing Feinstein for re-election as she faces a challenge from within the Democratic party. The California senator released a statement from Obama Friday, May 4, 2018, calling Feinstein one of the "most effective champions for progress." She's facing a challenge from state Sen. Kevin de Leon. (AP Photo/Pablo Martinez Monsivais, File)

House Speaker Paul Ryan of Wis., announces that he will not run for re-election at the end of his term, Wednesday, April 11, 2018, on Capitol Hill in Washington. (AP Photo/Jacquelyn Martin)

House Speaker Paul Ryan of Wis., announces that he will not run for re-election at the end of his term, Wednesday, April 11, 2018, on Capitol Hill in Washington. (AP Photo/Jacquelyn Martin)