Hillary Clinton defends her murky position on Iraq by saying she is working to pass a broad-based Senate resolution criticizing the president’s troop build-up. “I’m still in the arena,” she explains, “I’m still fighting to get those 60 votes.”

There, in a nutshell, is a key reason why only two sitting senators have been elected president in our entire history. Legislative leadership is an exercise in coalition-building. Blurring edges and making concessions is the only way to attract 51 votes (or 60 to break a filibuster). So individual lawmakers often support positions that don’t clearly and exactly express their own personal views.

Clinton talks about being “cursed with the responsibility gene,” but her bigger problem is the Senate gene. Just ask her fellow sufferer, John Kerry, how damaging that genetic handicap can be. His suicidal statement – that he actually voted against the Iraq war before he voted for it – was pure Senate speak. Senators often vote on both sides of an issue, depending on the amendments offered and the legislative package that eventually emerges.

But executive leadership is very different from legislative leadership. The best executives craft visions not coalitions, they paint in bright strokes, not pallid pastels. Almost every successful presidential candidate has already held an executive job – governor, general, vice-president (or in Herbert Hoover’s case, cabinet secretary). They have the habit of command not compromise.