Here we go again.

Lacking any control of the House schedule, Democrats have tried twice unsuccessfully in the past six months to use a discharge petition to force a vote on legislation they support. A discharge petition is a procedural tactic that allows an absolute majority of the House of Representatives (218 lawmakers) to force a floor vote on a bill, even if leaders who control the House floor oppose the measure. Successful use of discharge petitions conceivably could help the minority party hijack the majority party's legislative agenda.

But they rarely work, as Democrats have learned twice in the past six months. First they tried and failed to use one to force a vote on a plan to immediately reopen the government during the 16-day partial shutdown. Then they tried last month to force a vote on a proposal to raise the minimum wage.

On Wednesday, House Democrats rallied on the snow-covered steps of the U.S. Capitol to announce plans to try again, this time by filing a discharge petition to force a vote on a Democratic-backed immigration bill.

President Obama applauded his colleagues for their efforts, saying that "Immigration reform is the right thing to do for our economy, our security, and our future. A vast majority of the American people agree. The only thing standing in the way is the unwillingness of Republicans in Congress to catch up with the rest of the country."

But it won't work. Simply put, the math isn't there. The House Democratic caucus includes 199 members — 19 short of the votes needed for a petition to succeed. No House Republicans have said they plan to sign the petition and buck party leaders.

The math is even worse for the actual bill. The measure currently has a total of 200 co-sponsors — including three Republicans. But the Republicans won't sign the petition and six of the co-sponsors can't sign on because they are non-voting delegates from the District and U.S. territories. Three of the co-sponsors listed on the bill are no longer in the House: Rob Andrews (D-N.J.) has resigned, Mel Watt (D-N.C.) now runs the Federal Housing Finance Agency and Edward Markey (D-Mass.) is now serving in the Senate.

Even House Minority Leader Nancy Pelosi (D-Calif.) recently conceded that a discharge petition won't succeed in forcing a vote on immigration reform. "We'll never get to 218 on the discharge petition,” she told Sirius XM Radio’s Julie Mason at an event earlier this month.

But, Pelosi said, "outside mobilization is saying, 'All we want is a vote.'"

And that's the bigger goal of Democrats in this situation. They want to inspire outside groups, Latino voters and others pushing for reforms to hold it against Republicans during elections this fall. And Democrats know that immigration could become a flashpoint in a handful of competitive races in Arizona, California, Colorado, Texas and Florida, where the issue resonates. Will those races be enough to tip the scales in their favor? No. But Democrats will do anything they can to get closer to 218.