​Will the U.S. raise the minimum wage to $15?

The "Fight for $15" faces a heck of a fight.

The labor movement on Tuesday staged its largest rally to date, holding 270 strikes and demonstrations across the U.S. in an effort to win support for a nationwide minimum wage of $15 an hour. So far, the Fight for $15, which is backed by the Service Employees International Union, has hit upon a successful strategy of targeting cities and states where workers are struggling with high costs of living.

The next step -- the battle to raise the federal minimum wage -- could prove more challenging. The debate has stalled on Capitol Hill, with President Obama's proposal to boost baseline hourly pay to $10.10 failing to gain traction.

Because of inflation, the country's current minimum hourly wage of $7.25 has lost 8.1 percent of its purchasing power since 2009, the last time it was raised, according to the Pew Research Center.

That the Fight for $15 has found a receptive audience in coastal cities isn't all that surprising, given the high cost of living in many of those locations. Because of soaring rents and other costs, politicians in cities such as San Francisco and Los Angeles have moved to guarantee a living wage for low-income workers.

"From a point of view for strategy, if you are trying to build momentum, you will start with places that are more gettable," such as cities with a high cost of living, said Yannet Lathrop, research and policy analyst at the National Employment Law Project, which supports higher wages.

More than 4 of 10 employees in the U.S. earn less than $15 an hour, including 96 percent of fast-food workers, according to NELP. Nine cities and states around the country have boosted hourly wages to $15.

But in Lathrop's analysis, it's not only America's costliest cities that will soon require a $15-per-hour minimum wage. Most Americans, whether they live in Alabama or New York, will need to earn at least $15 an hour to make ends meet by 2020, she said.

Others say the country has nearly reached that point. A living wage requires more than $14 per hour in every state, according to an analysis for the Alliance for a Just Society. The most expensive state is Hawaii, where the group estimates it takes $21.44 per hour to provide a living wage, while the most affordable is Arkansas, where a living wage is estimated at $14.26 per hour.

The Fight for $15 is clearly aiming to gain support during the 2016 presidential election, with the organization describing low-wage workers as a voting bloc. In an emailed statement, the organization said it was "vowing to drive the nearly 64 million Americans paid less than $15 to the ballot box."

Some workers are gaining confidence that their efforts can make a difference, said University of Notre Dame labor law expert Barbara Fick. In a statement, she said, "It appears that the movement now is starting to have another ripple effect -- political action. Low-wage workers are beginning to see that together they can have an impact on how the system works."

Still, the kind of lower-paid workers who stand behind the Fight for 15 have a poor record of showing up at the polls, with researchers failing to find any election where low-income voter turnout was higher than that of wealthier voters, according to Demos.

By contrast, 99 percent of America's top 1 percent of earners voted in the 2008 election, compared with only 49 percent of those earning less than $10,000 per year.

The campaign also faces powerful opposition in Washington from organizations such as the U.S. Chamber of Commerce and the National Restaurant Association, which argue that raising the minimum wage to $15 will hurt small businesses and stifle job-creation.

"This conversation will spread more than it has to the federal level in the next year or so, and even beyond the elections in November," Lathrop said. "I don't think we can go back to $10.10 or $12. The conversation will be centered around $15."