“What the hell’s the presidency for?”

That was President Obama speaking on Thursday, quoting former president Lyndon B. Johnson. Obama was in Austin at the three-day conclave marking the 50th anniversary of the Civil Rights Act of 1964.

Seeking to capture the essence of Johnson and his presidency, Obama revealed something about his own.

Johnson was a larger-than-life figure when he was president. In memory, he has sometimes become an even larger presence, one that has been a source of both inspiration and exasperation to those around Obama. The question they hear so often is: Why can’t this president be more like LBJ?

Commentators on cable television talk about it all the time. They say Johnson possessed legendary powers of persuasion and a mastery of the legislative process, and they contrast LBJ’s successes in Congress with those of a president whose legislative agenda has repeatedly stalled and whose relationships on Capitol Hill are notably lacking.

During the 2012 campaign, Obama’s advisers heard the same thing in focus groups with sympathetic voters. These voters had no truck with the Republican tactics of obstruction, but they wondered why Obama lacked whatever LBJ had. Why couldn’t Obama make the machinery work better? Why couldn’t he cajole and threaten and sweet talk and bully the Congress into action the way Johnson had?

Obama is a far different person than Johnson. He is cool, cerebral and detached. Johnson was the earthy, insecure political seducer. Still, it is questionable whether even LBJ could be LBJ in today’s polarized political climate. Could he really have found a way to bring tea party Republicans to the bargaining table with any more success than has Obama? Even some who have studied Johnson’s presidency wonder.

Johnson’s legacy

On Thursday in Austin, Obama was face to face with Johnson and all his powers. Vietnam still haunts Johnson’s legacy, but this was a celebration of LBJ’s singular achievements on the domestic front and the civil rights gains that are universally acclaimed.

The president recounted a story told in “The Passage of Power,” the fourth volume of Robert A. Caro’s magnificent biography of Johnson. A few days after the assassination of President John F. Kennedy, Johnson was in conversation with aides about the speech he would deliver to a joint session of Congress the next day.

Johnson wanted to urge Congress to pass the most sweeping civil rights bill since Reconstruction. His advisers cautioned against it. “They said it was hopeless, that it would anger powerful Southern Democrats and committee chairmen, that it risked derailing the rest of his domestic agenda,” Obama said.

One adviser said the president should not waste his time on lost causes. “To which, it is said, President Johnson replied, ‘Well, what the hell’s the presidency for?’ ” Obama said to laughter and applause. He repeated the line for emphasis. “What the hell’s the presidency for,” Obama said, “if not to fight for causes you believe in?”

Disappointed liberals, conservative critics and ordinary citizens who remember the candidate of 2008 have asked that question about Obama’s presidency. What has he been willing to fight for? What are the causes he truly believes in? What risks has he taken?

As he stood at the lectern at the LBJ Presidential Library, it seemed obvious that Obama would have a ready answer for his critics: the Affordable Care Act. Like Johnson, Obama was told by some of his advisers to back away, to lower his ambitions, to seek something far smaller than the comprehensive bill that was in deep trouble on Capitol Hill. Obama rejected the advice.

Obama said he believed Johnson had come to the conclusion that he was the only person who could get a civil rights bill enacted in those times. Obama believed that, if health care did not pass in those first years of his administration, it could be another decade or more before a president could safely try again.

Obama said of Johnson, “And he knew there would be a cost [to passing a civil rights bill], famously saying the Democratic Party may ‘have lost the South for a generation.’ ” Johnson was correct about that. After he left office, Republicans held the presidency for 20 of the following 24 years, and the South became solidly Republican.

Obama put his party at risk with the passage of the Affordable Care Act. Opposition to the law alone did not decide the 2010 elections, but it was a significant factor and still is in today’s political debates. Republicans believe they can make gains this fall on the strength of opposition to the law.

The health-care law may be on more solid footing than it was a few months ago. The departure of Health and Human Services Secretary Kathleen Sebelius offers the administration the opportunity for a fresh start with some Republicans in Congress. But the political battle continues almost unabated.

What’s ahead?

Standing on the stage in Austin, Obama must have thought about how his own presidency and his singular domestic achievement will be seen in half a century. Will the Affordable Care Act be remembered as Medicare is today, as one of the most important social programs in the history of the country? Or, as conservatives claim and some liberals fear, will it be regarded as the initiative that ultimately set back the case for activist government for a generation?

Johnson didn’t stop with the 1964 Civil Rights Act. As Obama noted, he followed up with the Voting Rights Act in 1965. He took advantage of huge Democratic majorities in Congress to enact landmark social welfare legislation, including Medicare and Medicaid.

Obama followed the passage of health-care with another controversial, comprehensive measure, the Dodd-Frank financial reform bill. His second term has been marked by setbacks, controversies and disappointments. Beyond immigration reform, his legislative ambitions are few in number. Many of his followers are disappointed or disillusioned by what they’ve seen.

Another passage in the Austin speech seemed to capture the frustrations, or perhaps the realities, of Obama’s second term. He repeated what he had earlier said to David Remnick, editor of the New Yorker magazine, for a profile of the president that was published in January. Call it a lowering of ambitions or change in the time horizon for success.

“Those of us who have had the singular privilege to hold the office of the presidency know well that progress in this country can be hard, and it can be slow, frustrating and sometimes you’re stymied,” he said Thursday. “The office humbles you. You’re reminded daily that in this great democracy, you are but a relay swimmer in the currents of history, bound by decisions made by those who came before, reliant on the efforts of those who will follow to fully vindicate your vision.”

Johnson’s presidency will always be shadowed by the tragedy of the Vietnam War and the domestic civil unrest it triggered. But his domestic achievements now compete for attention in the shaping of his legacy, though as Obama noted, the Great Society remains a source of debate and disagreement 50 years on.

The record of Obama’s presidency is still incomplete. How much more will his remaining days in office answer the question Johnson posed with such passion half a century ago?