Brezhnev

Hint 1 of 5:

Mason - Scorpio thought Mason had killed McBain, but changed his mind.

Hint 2 of 5:

Leeland - It wouldn't be good if he became president.

Hint 3 of 5:

Thunderbolt - will cause a serious crisis in the world if it continues.

Hint 4 of 5:

Scorpio - wants to speak to you. You'll find him in Venice.

Hint 5 of 5:

Jackal - talk to Scorpio about him.