Not surprisingly, numerous Democratic Senators have come out against eliminating or scaling back the Senate's supermajority requirement:
Five Senate Democrats have said they will not support a lowering of the 60-vote bar necessary to pass legislation. Another four lawmakers say they are wary about such a change and would be hesitant to support it. ...
“It won’t happen,” said Sen. Dianne Feinstein (D-Calif.), who said she would “probably not” support an effort to lower the number of votes needed to cut off filibusters from 60 to 55 or lower.
Sen. Daniel Akaka (D-Hawaii) echoed Feinstein: “I think we should retain the same policies that we have instead of lowering it.
“I think it has been working,” he said.
Most Democratic Senators, especially older ones, are institutionalists. They believe in the Senate as a rarified place of bipartisanship and thoughtful compromise. They also have come to value rules that increase the power of individual Senators, who are like Gods in Washington compared to mere members of the House.
In reality, the Senate does not function in anything like the idealized way that Senators imagine. It's the House with a supermajority requirement (except for the budget.) Here's Jon Tester:
“I think the bigger problem is getting people to work together,” he said. “It’s been 60 for a long, long time. I think we need to look to ourselves more than changing the rules.”
It's been 60 since 1975. And for the majority of that time, the filibuster was a weapon of strong protest, not a routine supermajority requirement. But the old rare use of the filibuster was an unstable equilibrium. You can't have a competitive system where one side can use its most powerful weapon anytime it chooses but is expected not to do it that often. If baseball teams were allowed to deploy two extra fielders any time they wanted, but were expected to save the move for moments when they really needed a stop, how long would it take before every team always deployed 11 fielders?
The rare use of the filibuster survived as long as it did because the legacy of Jim Crow created an odd arrangement where party ties did not correspond to ideology. That era is not going to return. The political environment is competitive and parties are not going to leave a weapon lying on the ground.
That's why the filibuster's days are numbered: The majority does have the power to change the rules at the outset of a session. Democrats will make this notion a part of the party litany and demand it of candidates, and eventually the older Senators will be replaced by younger ones. More likely, the Republicans will simply change the rules first. This will happen the next time Republicans gain control of the White House, the House of Representatives, and more than 49 but fewer than 60 Senate seats. The old institutionalist concept of the Senate is mostly dead on the Republican side anyway. Gaining control of the White House and both chambers of Congress simultaneously is pretty hard to do anyway. There's no way Republicans are going to allow Democrats veto their agenda in such circumstance out of loyalty to a 1970s-era compromise.
Update: See also Jonathan Cohn's take.