Bruce Reed is right: holding the Presidency and a solid working majority in the House, Democrats can get a lot done without 60 Democratic Senators.
But there’s one thing they could do with such a majority, and probably not without one: abolish the filibuster, along with the other super-majority rules in the Senate (e.g., to pass a tax increase). [Wrong! See update below.] Yes, there are times that a 60-vote supermajority requirement helps liberal causes. But they’re few and far between. Mostly the filibuster helps the right.
Moreover, the Senate is so profoundly undemocratic to start with due to the over-representation of rural states that we should be very wary of rules that make it even more undemocratic.
But since any proposal to abolish the filibuster is itself filibusterable, you need 60 votes to get rid of it. It’s not impossible that we could get one or two moderate Republicans to support such a change; still, it’s better to be able to rely on your own. If abolishing that rule is within reach, I hope Reid goes for it.
Update A reader points out that Rule XXII (the filibuster rule) requires a two-thirds vote – among those present and voting – to change Rule XXII itself. Dammit, I knew that! Wishful thinking is a terrible thing.