We wouldn't need Olympia Snowe if the president simply told the Dems to vote the right way

I was talking to a politically astute friend the other day about health care reform and Olympia Snowe, and I asked her, "could Obama get 60 Democratic votes on health care reform?" She answered: "Sure, like this." Then she poked her finger at me. Huh? All he has to do, my friend then told me, is call up the Senators and tell them how to vote. In particular, Mary Landrieu (who needs a threat) and Ben Nelson (who needs an incentive). In other words, the president of the United States of America has a quite significant ability to get his way on legislation, if he wants to. Then why isn't he?