Chicago -- Barack Obama got out of the car a block early so everyone would see him walk to the picket line.

With a gray BlackBerry holstered between black pants and white dress shirt, the candidate immediately inserted himself into the rotating loop of striking hotel workers on Michigan Avenue. He shook hands, slapped backs and sang some lines of a pro-union chant. One worker handed him a "Unite Here!" placard, and he happily waved it above his head. Minutes later, as more than a dozen television cameras and reporters watched intently, he traded it in for a bullhorn.

"You are going to have a friend in the White House who believes that workers can organize," Mr. Obama shouted to the workers. "Who believes in union."

The crowd cheered, and after a Spanish translation, cheered again.

With more primary money in the bank than fund-raising juggernaut Hillary Clinton, Mr. Obama has now set about the more fundamental business of cementing the loyalty of the Democratic Party base. The $33 million he raised in the second fund-raising quarter from a record 258,000 individual donors gives him fuel to chase Mrs. Clinton and begin to close the sizeable leads she holds in surveys of many key primary states. But to do that, he needs the backing of organized Democratic constituencies whose can translate their support into votes.

"I think some of it is that the campaign is starting to heat up so you are starting to see more events like this," Mr. Obama said at a press conference following the union event on July 16. "What is true is that in the first two or three months you are so busy building infrastructure that sometimes your schedule gets much more crowded. And we are now in the phase of the campaign where people are listening much more carefully and we have the opportunity to amplify these critical issues."

Those critical issues -- unionization, gun control, civil rights, progressive taxation and abortion rights -- just happen to be the traditional linchpins of Democratic politics. And Mr. Obama, who likes to say that he believes in a different kind of politics, is tackling them aggressively.

On July 12, he co-sponsored legislation in the Senate to close a tax loophole that permitted hedge fund investors, who happen to be some of the most generous contributors to his campaign, to pay levies on billions of dollars in profit at a lower rate than most income earners. The issue, which was first raised by John Edwards, put pressure on the rest of a Democratic field that enjoys lucrative support from the wealthy financiers. On July 13, after originally giving a noncommittal answer, Mrs. Clinton also said she supported taxing the investors like regular corporations.

"I think it should be a no-brainer issue for Democratic and Republican candidates," Mr. Obama said when asked why not everyone had jumped on the issue immediately. "The way our tax code is now structured has exacerbated inequality in the society."

Mr. Obama's emphasis on traditional base-consolidation was illustrated nicely by a flurry of events aimed at key Democratic constituencies in mid-July

On a Sunday morning, Mr. Obama's motorcade arrived at the Vernon Park Church of God in the beleaguered Far South Side of Chicago. In the blocks around the church, bored-looking boys walked around with jeans cinched around their thighs under long white T-shirts. A woman in a wheelchair propelled herself against a red traffic light using her one good foot like a skateboarder. Abandoned lots surrounded empty restaurants with names like "Steaks and Lemonade." Here, gun violence had touched many residents personally, including the church's own pastor, whose mother and brother were murdered.

Mr. Obama had come to express outrage, as he uniquely can in this election, about the pall of gang violence that hangs over many black communities. Before speaking, he sat in a dark suit and blue striped tie under one of two large screens that said "Responsive Reading. Benefit of Obedience." He bobbed his head as a gospel choir sang to the organ and drums. When he was introduced to speak, the crowd erupted in cheers and hoots and the padded clapping of ushers in white gloves.

Mr. Obama has at times disappointed on the stump with seemingly deliberate displays of oratorical restraint, especially in front of audiences that tend to see him as the race's most charismatic candidate. But in black churches, like in Selma back in March and here in Chicago, he has tended to display the full sweep his rhetorical skill.

On that Sunday, he used it to attack enemies of gun control and the prosecutors of the war in Iraq, two issues central to the black voters who will be decisive in picking the party's nominee.

From the pulpit, he advocated the permanent reinstatement of a ban on assault weapons and more stringent regulations on gun dealers.

"And there is only one reason that hasn't been done and that is the power of the gun lobby in Washington," said Mr. Obama. Talking about the cultural differences between gun users in inner cities and rural settings, he said he recognized that many gun owners "want to hunt with their fathers, they want to hunt with their sons. I respect that. If you want to go hunt, go hunt. Nobody is trying to take your rifle or your shotgun away."

But, building to a crescendo, Mr. Obama added, "It is time for us to stand up and say enough. Enough to the gun lobby -- we're not going to take it no more."

(A man in the crowd called out "Preach, Mr. President," at which point Mr. Obama promptly seemed to reign himself in.)

Before he finished, he made sure to insert some references to the Iraq war, which has been perhaps the single most galvanizing issue so far in the primary. Mr. Obama opposed the war from the Illinois State Senate in 2002 and does not carry the burden of having voted for its authorization, as Mrs. Clinton and Mr. Edwards do. He has used that advantage to curry favor with the antiwar bloc, but has recently stepped up his criticism of the administration, and of Mrs. Clinton, whose plan to stop the war he has called "convoluted."

Obama told the 300 church-goers and seven television cameras that the war was depriving inner cities of much-needed recourses. "We are spending $275 million a day to try to keep people from killing each other in another land," he said from the pulpit, "right when a war is being fought right on the streets of Chicago."

Less than an hour later, Mr. Obama was standing in downtown Chicago, in front of an association of the country's leading trial lawyers, a traditional Democratic cash cow, brandishing his Harvard Law School and constitutional law credentials and decrying what he called the Bush administration's abuses of justice.

"Special interests are trying at every step to close courtroom doors to people who have been injured and defrauded out of their life savings," said Mr. Obama, to the members of the American Association for Justice (formerly the Association of Trial Lawyers of America -- itself a special interest group reviled on the political right).

"If we hope to break the special interest cycle, if we hope to truly transform this country, if we hope to live up to the ideals of opportunity and fairness and equality, that animated the life of this nation, then we have to change our politics too," he said.

But Mr. Obama's changed politics, in many ways, looks a lot like the traditional Democratic route to the nomination. Union organizers on that Monday said that his picket-line march, which Mr. Obama took care to say was not a political "stunt," could well help him with the powerful hotel workers union in Nevada, an early primary state.

Officials in the campaign said that Mr. Obama would be using the $33 million in second-quarter donations to make more campaign forays into the early primary states. And he'll continue to show up at events like the one on July 17 organized by Planned Parenthood, the women's abortion rights group. (Mr. Edwards' wife, Elizabeth, and Mrs. Clinton also attended.)

When asked on the following Monday how he could catch up to Mrs. Clinton, who he trails nationally and in every primary state but South Carolina, Mr. Obama seemed confident that his efforts to reach out to the base would be successful.

"We're not worried about polling. At this point we're worried about building enthusiasm at the grass roots," he said above the clamor of the striking hotel workers behind him. "The fund-raising is an expression of the enthusiasm at the grass roots level. That's why we've got 258,000 donors."

This article first appeared in the New York Observer and is reprinted with permission.