Before 2009, most Americans never heard of Sens. Ben Nelson, Max Baucus or Kent Conrad. More have heard of the Independent Sen. Joe Lieberman as a result of his Democratic vice presidential bid in 2000.
Yet now they are the movers and shakers in the Senate. Anyone who follows politics knows exactly who they are. It could not be further from 2005 when Nicholas Confessore in The New York Times wrote that "centrist Democrats today struggle with an unfriendly environment."
Throughout the Senate debate over health care, the centrists repeatedly forced the president's hand by insisting on changes to the legislation that made Obama's liberal base furious and which will constrain the impact of this legislation. Health care was the second major victory for centrists this year. They also were able to cut down the size of the economic stimulus bill back in February 2008.
Why is this small group of senators so influential and will this change? The first reason has to do with the nature of the Democratic Party. Democrats have never been as ideologically disciplined as the Republicans, and they have been less successful containing party differences.[...]
The second factor behind the new kings of the hill has to do with the sharpening of the partisan divide on Capitol Hill. The impact of growing party polarization since the 1970s has meant that winning votes from the other party is extraordinarily difficult. Except for rare moments, neither party can count on winning significant blocks of votes from the other side of the aisle.[...]
Finally, institutions matter. The U.S. now has a Senate that operates as a supermajority. The Senate now requires 60 votes on any piece of legislation given that senators are willing to use the filibuster on almost any bill. If the majority party needs 60 votes to pass a bill, and it can't win votes from the other side, a handful of moderates wield tremendous power.
The second option would be to use the power of the bully pulpit, as well as the famous but now forgotten campaign network from 2008, to go into the states of these senators and build grassroots pressure to vote with the party. Thus far, the president has been hesitant to take this path.