FILE - In this Nov. 6, 2018, file photo, Rep. Beto O'Rourke, makes his concession speech at his election night party in El Paso, Texas, after being defeated by Sen. Ted Cruz, R-Texas. One of the largest outside Democratic groups says ramped up spending on digital advertising played a key role in midterm battleground races, offering a lesson for potential presidential contenders in 2020.(AP Photo/Eric Gay, File)

FILE - In this Oct. 28, 2018, file photo, Sen. Cory Booker, D-N.J., speaks at a get out the vote event hosted by the NH Young Democrats at the University of New Hampshire in Durham, N.H. Motivated by an urgency to unseat President Donald Trump and the prospect of a historically large primary field, Democrats see little incentive to delay or downplay their 2020 presidential hopes. (AP Photo/ Cheryl Senter, File)

Sen.-elect Josh Hawley makes his victory speech while his wife Erin looks on during an election watch party Tuesday, Nov. 6, 2018 in Springfield, Mo. (AP Photo/Charlie Riedel)

FILE - This combination of Sept. 21, 2018, file photos shows Republican U.S. Sen. Ted Cruz, left, and Democratic U.S. Rep. Beto O'Rourke, right, during their first Senate debate in Dallas. Win or lose Texas' high-profile Senate race on Tuesday, Nov. 6, both Cruz and O'Rourke probably still have bright political futures, perhaps even plausible White House aspirations. (Tom Fox/The Dallas Morning News via AP, Pool, File)

FILE - This Oct. 20, 2014 file photo shows George Stephanopoulos at the 24th Annual Broadcasting and Cable Hall of Fame Awards in New York. ABC News says it is getting a one-hour jump on its rivals covering midterm election night results. The network will start at 8 p.m. Eastern time with Stephanopoulos as anchor on Nov. 6, 2018. Both CBS and NBC News previously said their continuous coverage would begin at 9 p.m. (Photo by Evan Agostini/Invision/AP, File)

The audience cheers as President Donald Trump arrives at Elko Regional Airport, Saturday, Oct. 20, 2018, in Elko, Nv., for a campaign rally. (AP Photo/Carolyn Kaster)

President Donald Trump speaks at a campaign rally Friday, Oct. 19, 2018, in Mesa, Ariz. Trump is in Arizona stumping for Senate candidate Martha McSally. (AP Photo/Matt York)

FILE - In this Wednesday, Aug. 8, 2018, file photo, U.S. Sen. Elizabeth Warren, D-Mass., speaks during a town hall-style gathering in Woburn, Ma. A DNA analysis done on Sen. Warren provides strong evidence she has Native American heritage. She provided her test results to The Boston Globe for a story published Monday. (AP Photo/Charles Krupa, File)

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)