The main point, other than their shared support of the Iraq War, is this recent quote from Ms Clinton about the experience of the presumptive Republican nominee (to the detriment of the presumptive Democratic nominee):
It's time for John Edwards and anyone else with a constituency in the Democratic Party to make a formal endorsement of Barack Obama. Now. They can no longer afford to wait the five and a half weeks until her next "firewall" in Pennsylvania on April 22. The divisive racial politics of her surrogates, and her direct questioning of Barack Obama's credentials, has gone beyond the pale (it's not Barack's fault that he didn't have the "experience" of being married to a President for eight years, privy to all [well, almost all] the President's secrets).
"I think that since we now know Sen. McCain will be the nominee for the Republican Party, national security will be front and center in this election. We all know that. And I think it’s imperative that each of us be able to demonstrate we can cross the commander-in-chief threshold,” the New York senator told reporters crowded into an infant’s bedroom-sized hotel conference room in Washington.
“I believe that I’ve done that. Certainly, Sen. McCain has done that and you’ll have to ask Sen. Obama with respect to his candidacy,” she said. [read more here]