As his presidency approaches the half-year mark, Barack Obama is on pace to be the most successful Oval Office occupant in more than half a century when measured by his ability to get Congress to vote his way "” even though he shows signs of carefully picking his fights on Capitol Hill.

Almost without exception, presidents start strong in their contests with lawmakers, and their success rates falter over time. Typically, presidents win most often in their first or second years in office on House and Senate roll call votes in which they take a clear position.

So far, Obama has taken clear positions on relatively few floor votes "” 26 in the House and 37 in the Senate, including 20 votes to confirm his nominees. Still, his success score of 95.2 percent, if it...