In a speech this week in Indiana, President Barack Obama announced a major shift in his position on Social Security. “It’s time we finally made Social Security more generous and increased its benefits,” Obama declared, “so today’s retirees and future generations get the dignified retirement that they have earned.”

This is a welcome change from Obama’s past support for a so-called Grand Bargain that likely would have included cuts to Social Security benefits. It is tempting to view it as evidence of how Obama “really” thinks about the issue, in the same way that his support for gay marriage, after years of opposing it, was seen as a reflection of his real views. But the shift on Social Security isn’t about Obama per se. Rather, it’s an excellent example of how political pressure from below can facilitate change. It also demonstrates the limitations of a president’s ability to impose his vision on the country.

Until 2014, Obama’s budget proposals included an offer to reduce the growth of Social Security benefits by changing how the cost-of-living increase is calculated, in exchange for a deal including upper-class tax increases. Obama, in other words, has not only dropped even contingent proposed cuts, but is also calling for an expansion of benefits. This is a big deal.

Admittedly, on a substantive level, it isn’t much different from his previous position. Tying “chained-CPI” Social Security cuts to upper-class tax increases no Republican Congress was ever going to pass was an indication that Obama was not actually trying to cut Social Security. The idea was to propose “entitlement reforms” that Beltway journalists tend to love in a form that would ensure Republican rejection. I happen to think this was dumb politics—no special effort is required to make the Republican conference look rejectionist, and being even theoretically open to such cuts weakens the Democratic brand and diminishes the ability of Democrats to attack Republicans for going to war on Social Security. But there’s no reason to believe Obama had any particular commitment to cutting Social Security.

What has changed, then, is the politics. The leader of the Democratic Party believes it’s in his political interest to support expanding rather than cutting Social Security. The pushback against chained-CPI from both Democratic voters and many congressional Democrats was crucial in making this happen. And you can bet Obama has been paying attention to Bernie Sanders’s strong presidential run, too, which has shown there is an appetite for a stronger welfare state. He changed his public position on Social Security for the same reason he belatedly came out in support of same-sex marriage rights: that’s where the party was.