As Barack Obama seeks approval for a military strike in Syria, he finds the footprint of his historic presidency shrinking.

It’s the fate of most second-term presidents as it becomes harder to keep public support and win legislative fights while their power wanes. For Obama, it’s arrived early.

He has implored Congress, the American public and U.S. allies around the world to support a military strike in Syria to deter its use of chemical weapons, yet even many fellow Democrats have failed to rally to his call.

In some respects, he circumscribed the office by design, saying on Sept. 4 that after the wars in Iraq and Afghanistan “it is important to get out of the habit of letting the president stretch the boundaries of his authority.”

He has much at stake in testing that theory. If he loses the vote on Syria, the Republicans will be emboldened to challenge him on fiscal issues, immigration and on his nominee to be chairman of the Federal Reserve. If he orders military action without congressional approval, at least one Republican House member, Duncan Hunter of California, said impeachment would be warranted.

If Obama wins, his position on those issues, along with immigration, will be strengthened just as he also is starting enrollment for his health-care law.

“Shrinkage is the lot of a re-elected president,” said John Pitney, a professor of politics at Claremont McKenna College in California and co-author of “After Hope and Change,” an analysis of the 2012 election. “A second-term president no longer has the power of novelty.”

Sized Up

“Sometimes, a first-year president gains the upper hand because lawmakers think that he or she may represent some larger political force. By year five, they’ve sized up the person in the Oval Office, and are a lot harder to intimidate,” Pitney said.

Beyond Syria, Obama has unusual competition for attention so early in a second term. His former campaign rival and secretary of state, Hillary Clinton, has often been in the spotlight as much as the president, all over the question of whether she will seek to replace him — more than three years from now. She will speak tomorrow in Philadelphia just before the president addresses the country.

Domestic Concerns

He also is finding the argument that the U.S. is the world’s indispensable nation isn’t having the same resonance it once did, with Americans more concerned about domestic issues such as the economy. And abroad, where Obama’s approval ratings are consistently higher than at home, he has been able to generate only modest support for taking action in Syria.

To be sure, the president could reset his standing, either by his own actions or world events that force it. In five television interviews scheduled for today and in his speech tomorrow, Obama will try to persuade the public that the U.S. must stand behind its assertion that the use of chemical weapons by the regime of Syrian President Bashar al-Assad requires a military response.

“There is a growing recognition that the world cannot stand idly by” and “there needs to be a strong response,” Obama said Sept. 6 during a news conference at the close of an international economic summit in Russia.

‘In the Game’

Tad Devine, who has advised several Democratic presidential candidates, said Obama “is still very much in the game. He could soon be leading a high wire, military action in the Middle East which would showcase him as commander-in-chief.

‘‘And he has demonstrated a unique electoral appeal in 2008 and 2012. He personally turned out an ‘Obama Electorate’ that was younger and more diverse that any American electorate we have seen before,’’ he said.

‘‘If he can show members of Congress and his own party leaders that he can help to mobilize that electorate again, even without his name on the ballot, he will continue to have a lot of political capital beyond the enormous powers of the presidency,’’ Devine said.

Mobilizing younger voters, whose opposition to the wars in Iraq and Afghanistan helped propel Obama as an antiwar candidate in 2008, could prove difficult. The president’s effort to summon support for a Syria strike is failing with the American public so far as well.

A Pew Research Center poll released Sept. 3 showed that by a 48-29 margin Americans oppose military action, and only 29 percent of Democrats back launching missiles.

Kosovo Bombing

President Bill Clinton faced a similar issue in 1999 when he asked Congress to authorize air and missile strikes in Kosovo in cooperation with NATO. As the Washington-based Cook Political Report noted, the resolution passed the Senate 58-41, with Democrats providing 73 percent of the ‘‘yes’’ votes.

The resolution failed in the House 213-213 with 213 affirmative votes from Democrats. Clinton’s approval rating at the time was 60 percent, while Obama’s is 44 percent.

At the time, Clinton had the support of then-House Speaker Dennis Hastert of Illinois, a Republican. The House later passed a bill funding military operations in Kosovo. The bombing campaign started after the Senate vote and before the House one, according to

First-Term Record

While Obama, like most second-term presidents, isn’t the force he was, he can still point to accomplishments, including passage of a landmark health-care law that was upheld by the U.S. Supreme Court, saving the auto industry, pushing for tougher regulations on Wall Street, and steering the country through a financial crisis.

Since Obama took office in 2009, the economy has averaged 1.7 percent quarter-on-quarter economic growth and the Standard & Poor’s 500 Stock Index (SPX) has risen almost 95 percent. Unemployment (USURTOT) in August was 7.3 percent, the lowest in his term after rising as high as 10 percent in October 2009.

John Geer, chairman of the department of political science at Vanderbilt University in Nashville, Tennessee, said that while Obama has ‘‘hit some rough patches of late, that often happens to presidents in a second term.”

“I do not think his presidency is shrinking, just struggling as second termers tend to do,” Geer said. “If we start to get better and better job numbers, he will start looking better and better too.”