President Barack Obama’s popularity shows no sign of letting up. He’s a TV sensation. He’s an Internet sensation. He’s a magazine sensation. He’s just a sensation. But none of that will protect him from … his own party.

[IMGCAP(1)]Obama held a positive session last week with Senate Democrats on the budget and other issues. He is scheduled to chat up the House Democrats today. These Democratic lawmakers seem to genuinely admire their president.

But they do not fear him.

They criticize his initiatives in some manner almost every day. It’s a far cry from the relative lock-step support Republicans gave former President George W. Bush during the early days of his administration. And it begs an important question: Will Democrats jump ship with the same spring in their step as Republicans did when — as it inevitably will — the going gets tough?

Signs of some of the dissing to come were evident in January, before Obama took office, when Senate Majority Leader Harry Reid (Nev.) said, “I don’t work for Barack Obama.—

Much of the current chatter has centered on Obama’s budget, with Democrats more than a little concerned about how they will explain gargantuan deficits to the voters back home.

Centrists such as Sens. Evan Bayh (Ind.) and Jim Webb (Va.) have been heard muttering about the need for fiscal discipline.

Budget Chairman Kent Conrad (N.D.), who is close to Obama, nevertheless shook his head at the deficits Obama was running and curled them back in the Senate budget resolution proposed.

Sen. Ben Nelson (Neb.) can be found in the halls of the Capitol holding forth politely but determinedly to reporters about his concerns with the Obama budget.

Even Appropriations Chairman Daniel Inouye (Hawaii) has wondered aloud how much spending can be absorbed at once.

But the complaints haven’t been limited to moderates or the Obama budget. Liberal Sen. Russ Feingold (Wis.) said Obama was not going far enough to curb earmarks, accusing him of trying to “fine-tune a fundamentally flawed process.— He teamed with Obama’s vanquished opponent, Sen. John McCain (R-Ariz.), to begin a crusade for the return of the line-item veto.

Just Friday, Feingold questioned Obama’s new war strategy, saying, “The proposed military escalation in Afghanistan, without an adequate strategy in Pakistan, could make the situation worse, not better.—

Obama has gotten even more pushback on earmarks. In a recent White House meeting with senior Democrats, the president got an earful about how earmarking was a right of lawmakers he should stop trampling on.

“I don’t think the White House has the ability to tell us what to do,— House Majority Leader Steny Hoyer (Md.) told reporters.

And the irrepressible guardian of the Senate, Robert Byrd (W.Va.), fired off a letter last month to Obama skewering his metastasizing system of White House “czars,— who wield enormous power in areas such as health and energy but need not answer to the Congress.

The open questioning of the president contrasts markedly with the demeanor of Republicans in the months after Bush took office in January 2001. Republicans seemed less likely to stray from the fold and publicly take exception. K Street, with a pent up list of priorities, practically set up bleachers along the sidewalk to cheer on the president. The GOP feared upsetting its narrow hold on Congress and the White House.

The fury of Bush political guru Karl Rove, who kept careful score of what was said and done with respect to the president, was perhaps no less an inducement to be supportive.

Of course, the famous exception was former Sen. Jim Jeffords (Vt.), who bolted the Republican Party amid disagreement with Bush.

Ironically, part of the reason he left the GOP fold was the White House’s petty effort to enforce discipline on the tax cut. Jeffords helped nix Bush’s original proposal. The president, for his part, failed to invite Jeffords to the White House for a ceremony honoring the nation’s teacher of the year — as a leader on education he was always a guest — and mulled ending Northeastern milk price supports.

Of course, after the attacks of Sept. 11, 2001, the president mostly walked on water in GOP circles until the war in Iraq started unwinding on him.

Part of Obama’s problem is that his very ubiquitousness may be making his colleagues unafraid. Some of a president’s power derives from his mystique.

The office, with its ceremonial duties, conveys some of the regal air of a monarchy. Obama, who meets regularly with fractious Democrats and submits himself to regular town hall meetings and session with the press, looks much more like a British prime minister being bounced around at question time in Parliament than he does a king.

The sight of Obama yukking it up with Jay Leno or racing down Pennsylvania Avenue to suffer and soothe Members of Congress makes him seem more like us, but perhaps a bit too much so.

Maybe it reminds his friends at the other end of Pennsylvania Avenue that just a little while ago he was the junior Senator from Illinois.

Nelson insists that he and his colleagues have put the junior Senator thing out of their minds. “Once you’re the president, you’re the top dog,— he said. Nelson suggests the criticism is more about Obama’s own openness to hearing other views — and his ability to take it.

“I think he makes it clear that he knows Democrats are not monolithic,— Nelson said.

Presidential communications scholar Martha Kumar of Towson University notes that Obama personally lacks Bush’s penchant for rewarding friends and punishing enemies.

“He ran on a platform of calming things down and a willingness to listen to all viewpoints,— Kumar said. But she noted that in any case, “Senators have sent signals they’re not rolling over.—

Sen. Carl Levin (Mich.) suggests the eagerness for a good quibble has nothing to do with Obama at all.

“I think it’s because we’re Democrats,— Levin said.