Since the midterm elections, President Obama has taken decisive action on immigration reform, climate change and relations with Cuba. Now, the new Republican-controlled Congress has handed him another opportunity to act boldly - by leaving a legacy as a strong defender of Social Security.

House Republicans signaled this week that they are gearing up for a major clash over the country's most important retirement program. In a surprise move, they adopted a rule on the first day of the new session that effectively forbids the House from approving any financial fix to the Social Security Disability Insurance (SSDI) program unless it is coupled with broader reforms. That would almost surely mean damaging benefit cuts for retirees struggling in the post-recession economy.

Republicans see an opening for benefit cuts in the SSDI trust fund. It is under severe financial pressure and on track to be exhausted at the end of 2016, when 11 million of the most vulnerable Americans would face benefit cuts on the order of 20 percent.

The rational solution is a reallocation of resources from Social Security’s Old-Age and Survivors Insurance Trust Fund (OASI). Such reallocations have been done 11 times in the past, and funds have flowed in both directions. Shifting just one-tenth of 1 percent from OASI to SSDI would extend the disability fund’s life to 2033.

Instead, House leaders appear to be maneuvering to push through an SSDI fix during the lame duck session following the 2016 elections. Such an 11th-hour package would likely impose cuts to the retirement program, including higher retirement ages and reduced annual cost-of-living adjustments. Legislators wouldn’t have to explain a vote for benefit cuts to their constituents before the elections, and might avoid accountability if changes to Social Security get tacked on to an omnibus spending bill or other yearend legislation.

“I don’t know why this had to be done on Day One," said Cristina Martin Firvida, director of financial security at AARP. "It makes it much less likely that we’ll deal with the disability problem until the lame duck session - and that won’t provide a good result for American taxpayers.”

Critics say the disability program is rife with fraud, and out-of-work baby boomers too young for retirement benefits are freeloading by getting disability benefits. There's no doubt that a program the size of SSDI is subject to some abuse, or that reform may be needed.

But SSDI’s real problems are less sensational. They include more baby boomers at an age when disability typically occurs and more women in the labor market eligible to receive benefits. Meanwhile, the increase in the full retirement age now under way, from 65 to 67, adds cost to SSDI, as disabled beneficiaries wait longer to shift into the retirement program.

This throwing down of the gauntlet should send a loud, clear signal to Democrats: It’s time to reclaim your legacy as the creators and defenders of Social Security. A small number of progressive Democrats have embraced proposals to expand benefits, funded by a gradual increase in payroll taxes and lifting the cap on covered earnings, but most Democrats have been spineless, mouthing platitudes about "keeping Social Security strong" - a pledge that could mean just about anything.

Expansion is not only doable financially - it has overwhelming public support. A poll released last fall by the National Academy of Social Insurance found that 72 percent of Americans think we should consider increasing benefits. Seventy-seven percent said they would be willing to pay higher taxes to finance expansion - a position embraced by 69 percent of Republicans, 76 percent of independents and 84 percent of Democrats.

Congressional Republicans are way out of step with Americans on this issue, and so is the White House. The administration has been all too willing to flirt with benefit cuts as it chased one illusory "grand bargain" after another.

But the unbound Obama now has an opportunity to stiffen and redefine his party’s resolve on Social Security. The president should propose expansion legislation. Democratic presidential and congressional candidates should run on Social Security expansion in 2016 and work to assure that reform isn't tackled in an unaccountable lame duck vote.

In 2005 a young Democratic senator sized up Social Security politics during the debate over President George W. Bush’s plan to privatize the program:

“[People in power] use the word 'reform' when they mean 'privatize,' and they use 'strengthen' when they really mean 'dismantle.' They tell us there's a crisis to get us all riled up so we'll sit down and listen to their plan to privatize ...

“Democrats are absolutely united in the need to strengthen Social Security and make it solvent for future generations. We know that, and we want that.”

That senator was Barack Obama of Illinois.