It’s opposite to the way the press describes presidential elections, but it sure does seem like winning a larger margin of victory in a presidential election produces more centrist policy (even if the policy that is introduced is more likely to be enacted.) This isn’t really surprising, for two reasons:
a) If legislative action is on the table, the 60th Senator is the deciding vote, so Ben Nelson’s preferences on health care were more important than Obama’s own in shaping the ACA as it actually passed. If legislative action is off the table, Obama and his close advisors shape which executive actions to take.
b) Parties are coalitions of voters and interest groups representing (and attempting to influence) those voters. As more voters drop out of a coalition (for example Obama 2012 vs. Obama 2008), the remaining, more ideologically pure voters and interest groups have greater sway.
The conclusion to draw, I think, is that there’s really nothing wrong with judging a candidate by his or her supporters, and that if you lose, it’s actually better to lose big than to lose small.
(Yes, for most recent presidents except Obama, the more ideological term- and the more narrow electoral victory- was the first one, so the usual conclusion is that the first term is the time for “getting things done” while the second term is just coasting. But I think the explanation above- where narrow first term victories allowed for more concentrated support for ideological policy- makes more sense.)