It took Democrats 48 hours to break Sen. Richard Shelby’s hold on President Obama’s appointees. In that same short interval, Democrats also broke their own best excuse for their biggest failure.

The Senate allows its members to delay confirmation votes. This power is located not in the Constitution – not even in the Senate rules – but in the Senate’s own strange customs.

Senators use the power to extract favors. The president wants Jane Bloggs as assistant secretary of commerce? Senator Snorkum holds her hostage until he gets something in return. Not a pretty system, but familiar.

Shelby took an extra step. Unhappy about the administration’s failure to commit to spending projects in Alabama, Shelby placed a hold on every single appointee, including national security nominees. Democrats made an issue of the holds. Majority Leader Harry Reid denounced them on the Senate floor. Embarrassed, Shelby relented.

Senators may be arrogant, but they are also elected. They are sensitive to public opinion. If obstructionism looks politically dangerous, they do not obstruct.

Yet as health-care reform stalls, Democrats have taken to blaming Republican filibuster threats for their own troubles. If anything, the Democratic debate over the filibuster now seems more intense than Democratic enthusiasm for their own healthcare reforms. Democrats have not yet lost, but they are already shifting their attention and energy from the fight for health-care legislation to the search for health-care scapegoats.

As scapegoats go, the filibuster looks promising.

Democrats point out that Medicare was enacted in the 1960s with a simple majority. Back then, the filibuster was an extreme measure that usually failed. Since then, however, it has grown into a routine element of Senate procedure; a huge new grant of power to Senate minorities that has been deployed more often in the 2000s than in the 1990s, more often in the 1990s than in the 1980s. The crude joke on Capitol Hill is that it now takes 60 votes to pass a kidney stone.

Democrats are right that the filibuster has mutated wildly. But as the Shelby case demonstrates, there are still important limits, and one important limit above all, to procedural bottlenecks: public opinion.

If the president proposes something popular, the Senate will get out of the way -- filibuster or no. Democrats did not filibuster George W. Bush’s Medicare Part D, which created a popular prescription drug entitlement for the elderly. Republicans did not filibuster Bill Clinton’s law requiring insurers to cover 48 hours of maternity care. The problem for the president’s majority comes when the president proposes something unpopular. In that case, the minority gets very brave.

I’m not defending the filibuster here. Sometimes what is unpopular is also right and necessary. I’m only noting that the Democrats’ problem with health-care reform is not with the culture of the Senate. It is with the country – and with members of their own party.

The filibuster gives reluctant Democrats a perfect excuse for moving away from the president. “We’d love to be with you sir … but the GOP now has 41 seats, and we just can’t begin to figure out a way around that fact. So let’s drop the whole thing OK? Or postpone it until after our elections? Please??” They sound like lazy Boy Scouts inventing reasons to avoid the nature hike. “It’s cloudy – it might rain! No wait, the sun’s coming out and I forgot my sunscreen!”  If Senate Democrats really wished to adopt health-care reform, no way would they surrender so easily.

The poll numbers for health-care reform have tumbled over the past year. We can dispute why this is so: blame the bad economy or credit the town halls as you please. But it is so.

President Obama has said that he anticipated all along that health-care reform would be unpopular. That’s pure revisionism. Democrats have always thought of health-care reform as a winning issue – that’s why they wanted to put the negotiations on C-Span, remember?  So that “the people” would see who was on their side – and who sided with the detestable special interests?

Now the public has decided it does not want health-care reform so very badly – and suddenly the Democrats have decided that the detestable special interests stand 11 feet tall, and that muscling the Republican minority is a doomed, hopeless undertaking.

Go ask Richard Shelby about that. Then go find another excuse.