Lieberman might have some problems with his party after this summer

Zell Miller did this before and wasn't kicked out of the party, but I am sure that this will at least cause some tension:

McCain has yet to ask Lieberman to speak, either in primetime or elsewhere, at the convention. But if McCain thinks it will help make his case for the White House, as some of his allies suspect, Lieberman would be willing to speak on his behalf.
“If Sen. McCain, who I support so strongly, asked me to do it, if he thinks it will help him, I will,” Lieberman said in a brief interview.