Sometimes, silence can speak volumes.
Al Gore can’t publicly endorse Barack Obama. Its virtually unthinkable that he would publicly do that because it would be such a slap in the face to what essential amounts to his political family. But, by not doing anything he essentially says that he doesn’t support Hillary for President. There’s a case to be made that by not saying anything at all, Gore is giving Obama a silent endorsement. But because he can’t publicly endorse Obama we’ll never know for sure.
I can say this though, his silence has really spared Obama what would have been a devastating blow.