MIGHT BE A MORE EFFECTIVE STATEMENT...:

The choice of Kara-Murza, who says he has been poisoned twice, appears aimed at sending a last message to Putin and Trump, whom McCain had criticized for sounding too cozy with the Russian leader, amid an investigation into whether the U.S. president's allies cooperated with Moscow's efforts to intervene in the 2016 election.

For more than seven years, McCain and Kara-Murza had each other's backs as each criticized Putin and what they saw as his autocratic tendencies in Russia.

"We all knew this day was coming, but hoped against hope that it would not be coming so soon," Kara-Murza wrote of McCain's death in The Washington Post on Monday. "He was a true leader and a dear friend, and it will always be among the greatest blessings of my life to know him."

Officially, Kara-Murza, 36, who lives in the Washington area, is the vice chairman of the Open Russia movement and chairman of the Boris Nemtsov Foundation for Freedom, established in honor of the dissident political leader who, critics say, was assassinated in 2015 for his anti-corruption investigations into Putin.

Unofficially, with help from McCain, Kara-Murza has positioned himself as perhaps the biggest full-time thorn in Putin's side.

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