WASHINGTON (AP) — There's only so much that President Barack Obama can do to help his party this year. Six years in, he's less popular than before, and aside from fundraising, his value on the campaign trail is limited, especially in the places that matter most for Democrats.

But the president can set the tone — and in his State of the Union address on Tuesday, Obama will deliver the opening salvo in a yearlong fight for control of Congress. Although not explicitly political, the speech before millions will frame an economic argument that Democrats hope will resonate with voters in races across the country.

"It will be interpreted as the Democratic agenda," said Celinda Lake, a Democratic pollster. "He can frame up the 2014 choice."

That choice, as Obama portrays it, is between an America where all segments of the population have opportunities to improve their lot and one where prosperity is disproportionately enjoyed by a select few. In the run-up to the State of the Union, Obama has persistently sought to focus the nation's attention on trends of inequality and lower social mobility that he's pledging to address in his final years in office.

To be sure, not every Democrat will echo Obama's themes in their own campaigns. Many may focus on niche, regional issues or their personal characteristics. But with the economy still a top issue for most voters, Democrats see issues of economic fairness and expanding access to the middle class as their best chance to reach a broad swath of the population that feels left behind by the sluggish economic recovery.

"Middle-class security is the defining issue of our time," said Rep. Steve Israel, D-N.Y., who chairs the House Democrats' campaign arm. "Our candidates are going to talk about what priority makes more sense for the middle class: Increasing the minimum wage, or decreasing taxes for the wealthiest? Those contrasts are imperative and revealing."

When Obama invited Senate Democrats to a meeting at the White House this month, much of the session focused on how Democrats wanted Obama to focus on the notion of expanding economic opportunity in his State of the Union, said a White House official, who wasn't authorized to discuss a private meeting by name and requested anonymity. Obama's legislative affairs director, Katie Beirne Fallon, and his senior adviser, Dan Pfeiffer, consulted closely with Democratic leadership in the House and Senate as they planned the speech and this year's legislative agenda, the official said.

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Republicans also have taken notice of the public's interest. In recent weeks, lawmakers such as Sen. Marco Rubio, R-Fla., Rep. Paul Ryan, R-Wis., and Sen. Rand Paul, R-Ky., have publicly floated their own ideas about reducing poverty in the U.S.

For Democrats, Obama's message may fall short of the argument they'd hoped to be able to make in their sixth year in the White House, when the president's party historically takes an electoral drubbing.

But Obama's signature legislative feat, his health care law, remains unpopular across the country. Unemployment's still high. And with Congress bitterly divided and gridlocked, there are few other major achievements either party can point to as they ask voters to give them their support.

The idea is to rally Democrats behind an uplifting theme with broad appeal across geographic, demographic and partisan boundaries. In an AP-NORC Center for Public Affairs Research poll last month, 68 percent said they'd like the federal government expend a moderate or great amount of effort reducing the gap between rich and poor. By comparison, less than half wanted the government to focus on advancing gay rights or fighting climate change.

Finding a theme with cross-party appeal is especially critical for Obama's party this year, when Democrats are defending 21 of 35 Senate seats — many of them in Southern, conservative-leaning states where Obama's low approval ratings are likely to be a drag on fellow Democrats. As Democrats like Mary Landrieu in Louisiana, Mark Pryor in Arkansas and Mark Begich in Alaska seek distance from the president, you won't likely see him campaigning in their states his year. But he can focus the public's attention on what Democrats want to do to fight unemployment, improve education and boost wages — issues that resonate deeply in those same states.

Preserving Democrats' fragile majority in the Senate is of key concern to Obama, who would see any hope of moving any of his agenda through Congress evaporate should Democrats lose the upper chamber in November. Democrats are less bullish about their prospects for taking back control of the House, where Republicans hold a 233-200 advantage with two vacancies and are expected to retain their majority.

Republicans hope the renewed focus on the economic reality in the U.S. will offer an opportunity to showcase how Democratic ideas have failed to cure the very ills Obama and some Democrats lament.

"The president is now preparing speeches on income inequality. I believe he should give those speeches while standing in front of the mirror, because under his watch, everything has gotten worse," Republican National Committee Chairman Reince Priebus told a national GOP gathering. He cited poverty and dependency on food stamps as problems he said have gotten worse and led Americans to give up during Obama's presidency.

Sen. Chuck Schumer, D-N.Y., a leading strategist for his party, said the White House is coordinating closely with House and Senate Democrats on the timing and messaging for issues like a minimum-wage increase, which Obama has been pushing since last year's State of the Union. When Senate Democrats decide to put a bill on the floor to raise the minimum wage, for instance, Obama will be out holding events to shine a spotlight on the issue.

"We'd prefer to succeed in the legislation," Schumer said in an interview. "But if not, it will make a very persuasive case why people should vote for us in 2014."

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Reach Josh Lederman on Twitter at http://twitter.com/joshledermanAP