During the fight over healthcare reform, it was common for liberals to complain about “centrist” senators like Missouri’s Claire McCaskill or Nebraska’s Ben Nelson, who used their leverage as filibuster-breaking conservative Democrats to water down the stimulus package, healthcare reform and other liberal priorities.

With a few faces notwithstanding (Evan Bayh, who left the Senate, and Blanche Lincoln, who lost her re-election bid), those senators are still around, and they still present significant obstacles to progressive legislation. Here is Politico with the “centrist” reaction to the American Jobs Act, which promises to deliver much-needed stimulus to a faltering economy:

“Terrible,” Sen. Jim Webb (D-Va.) told POLITICO when asked about the president’s ideas for how to pay for the $450 billion price tag. “We shouldn’t increase taxes on ordinary income. … There are other ways to get there.”

“That offset is not going to fly, and he should know that,” said Democratic Sen. Mary Landrieu from the energy-producing Louisiana, referring to Obama’s elimination of oil and gas subsidies. “Maybe it’s just for his election, which I hope isn’t the case.”[…]

“Every dollar that is spent on the jobs bill…is not going to be available to Congress to deal with the debt,” said Sen. Joe Lieberman of Connecticut, an independent who caucuses with Democrats. “And to me, the top priority of ours should be long-term major debt reduction.”

Poor economic conditions are crucial to Democratic success next year, and conservative Democrats would be much better off with an American Jobs Act than they would without. Despite this, they insist on attacking the president and his proposals. As Matthew Yglesias points out, this behavior is almost unheard of among Republicans, even those that represent moderate and liberal states.

This dissent with the White House even extends to Democratic strategists and activists, who are increasingly dissatisfied with the president. Politico reports:

On a high-level campaign conference call Tuesday afternoon, Democratic donors and strategists commiserated over their disappointment in Obama. A source on the call described the mood as “awful”

“People feel betrayed, disappointed, furious, disgusted, hopeless,” said the source.”

With the exception of progressive lawmakers in the House (which isn’t insignificant), Democrats aren’t enthused about the American Jobs Act or President Obama’s broader effort to regain control of the conversation. This should tell us something—Despite his status as “party leader,” Barack Obama can’t control the actions of Democratic lawmakers, activists or elites, and his overall influence is limited by structural factors within and outside of the Democratic Party.

Last week’s speech was a fantastic defense of liberal ideas, but as is almost always the case, presidential rhetoric—even when it’s strong—does little to address the structural obstacles to better policy. In other words, the barriers to progressive policies are high, enduring and exist throughout the political system.