I'll also remind you that
both times Americans have elected Vice Presidents of parties other than their running mates, those Vice Presidents have succeeded to the Presidency. Andrew Johnson became President after Lincoln's assassination. He proved to be so much of a Democrat that the Republicans, who elected him Vice President, actually impeached him. John Tyler was so much of a Democrat that he was expelled from the Whig Party (to which he had nominally become a member for the purposes of the election).
John McCain is 72. Do you really want Joe Lieberman as your President?