In the days when monarchies ran nations a term that became notable was that of "marriage of convenience."

This element occurred when nations decided that it would be in their respective best interests to have prominent families from different nations join forces in matrimony for mutual political convenience.  It was a way of obtaining a geopolitical foothold into an additional nation at the very least and more through formation of alliances.

An alliance of modern political convenience occurred when veteran Senator Arlen Specter of Pennsylvania decided to switch parties and become a Democrat.  

Since Obama's political team was shrewd enough to catapult a junior  senator of four years of a national political career into the White House,  all essential points were covered in discussions with Specter and his team before the veteran solon made his announcement that has left Washington buzzing with speculation ever since.