Bob Schieffer has covered every presidential election since 1964. That's 14 and counting -- each one different, and none quite like this one. He sat down with "CBS Evening News" anchor Scott Pelley to share what he thinks the implications may be for the Republican party.

SCOTT PELLEY: What do you make of all this?

BOB SCHIEFFER: On the Republican side what we're seeing here is a changing of the guard. If Trump wins the nomination before the convention, and it looks like he probably will, it will turn the Republican party on its ear. If it goes to an open convention, it will be a bloody fight that could break the party into two parties. In either case, the Republican party we used to know will be replaced by something new. Exactly what that will be is uncertain, and that's the scary part. Because the one thing that never bodes well in politics, or economics, or national security matters is just that -- uncertainty.

PELLEY: Can Trump actually win the presidency?

SCHIEFFER:He could, but historically nominees who come from outside their party mainstream do poorly. When Republicans split over civil rights in 1964 and nominated Barry Goldwater, they went down to a historic landslide defeat. When Democrats kicked out party regulars and nominated George McGovern in 1972, he lost every state but Massachusetts. Under the old rules it would be coming down to a couple of basically flawed candidates -- but in today's politics who knows what that means or where this is going.