A coalition of some Republicans and nearly all Democrats is attempting to go around House GOP leaders and force a debate later this month on a series of immigration bills against the wishes of GOP leaders.

How do they do it?

The mechanism is called a “discharge petition.” A discharge petition is a rarely-successful gambit which requires the signatures of 218 House members, regardless of the size of current House. The House’s total membership is fixed by statute at 435. So, 218 is more than half of the House. 218 is usually the number needed to pass bills if all members vote. However, the House is now at 428 members due to resignations and a death. But the number of signatures for a discharge petition is locked at 218, regardless of the House’s size.

The House may only consider discharge petitions on the second and fourth Mondays of each month. If the House is out on one of the eligible days, supporters of the discharge petition are out of luck. The House used to operate on a strict “calendar” system, based days of the week. Each day held a particular “pedigree.” For instance, the House may consider certain types of bills on a “Wednesday.” Other categories of bills are only up “Monday through Wednesday.” Thus, a discharge petition was assigned the second and fourth Mondays of each month.

Supporters of a discharge petition on a given issue must secure the signatures of 218 members approximately seven days days where the House meets ahead of a Monday which qualifies.

Therefore, supporters of the current discharge petition on immigration and DACA need to secure 218 signatures by June 11. If they are successful, this discharge petition ripens on the fourth Monday of this month, June 25. The next crack at a discharge petition comes July 23. The House is out on the second Monday next month, July 9.

The House is not scheduled to be in session on any second or fourth Mondays the rest of the year, save December 10. But, Congress plans to be out of session for the year a few days later. No discharge petition may come up that late in a Congressional session.

Just today, Parkland, FL student David Hogg was on Capitol Hill touting a discharge petition for gun legislation. That’s well and good. But frankly, Hogg and gun control advocates are hamstrung by the House calendar. Hogg and others are out of luck unless something develops quickly on guns to meet the next two deadlines.

Because of these restrictions, it’s not hard to understand why there have only been two successful discharge petition efforts in the House in the last 16 years. One was on a campaign finance reform bill in 2002. The other was to reauthorize the Export-Import Bank in 2015. House leaders rarely lose control of the floor via a discharge petition campaign.

What happens?

Let’s say backers of the discharge petition marshal the necessary signatures this week. If that’s the case, then any signatory of the petition may ask to call it up on the House floor just after the Pledge of Allegiance on June 25. However, it’s possible the House could secure an agreement to consider the petition later in the day.

The merits and demerits of the discharge petition itself receive 20 minutes of debate on the floor.

But here’s where it gets tricky for this particular discharge petition.

Advocates of the effort aren’t discharging a solitary immigration/DACA bill to the House floor. They are discharging a framework for the House to consider a sequence of four immigration/DACA bills.

So, after the debate, the House will vote up or down on the petition itself. If the House votes in favor of the discharge petition, members begin an hour of debate on the framework to accommodate the four measures. The gig is up if the House votes against the discharge petition (which would be odd, considering the fact that supporters of the effort garnered the appropriate signatures).

Then the House votes on the structure for the four bills. Same process. If the House approves the framework, everything forges ahead. If the House rejects the outline, everything halts in its tracks.

Then, the House allocates 40 minutes apiece for debate followed by votes on each of the four immigration/DACA bills.

The first bill up is the conservative immigration plan backed by House GOP leaders and authored by Senate Judiciary Committee Chairman Bob Goodlatte (R-VA). Then the House considers the Democrats’ DREAM Act, backed by Rep. Lucille Roybal-Allard (D-CA). Next in the queue is whatever bill House Speaker Paul Ryan (R-WI) elects to to put forward. Finally, there’s a plan supported by Reps. Jeff Denham (R-CA), Will Hurd (R-TX) and Pete Aguilar (D-CA). That bill bolsters border security and grants legal status to many DACA recipients.

But things get a little weird again at this stage.

The blueprint under which the House is considering the four bills is known colloquially as “queen of the hill.” In baseball, this would be the equivalent of the National or American League Championship Series. Whichever bill obtains the most votes (not necessarily 218) advances to the next round. In other words, the World Series. That bill is “queen” but not yet “king.”

A short procedural debate and vote then unfolds (called a “motion to recommit,” the final method used by opponents to kill bills and return them to committee). Then the House votes to pass or fail the bill designated “queen” to see if it in fact “king of the hill.” Or, in baseball parlance, that legislation wins the World Series.

The only difference is this: there’s a World Series champion every season (with the exception of the 1994 strike year). With “queen of the hill,” a bill doesn’t always graduate to king. A bill is not guaranteed passage at the king level even though it “won” at at the lower round.

House Republican leaders are scrambling to work out an agreement on immigration before discharge petition advocates can collect the necessary signatures and propel this process onto the floor. The GOP brass plans a big conclave on immigration Thursday morning.

House GOP leadership is adamant that there won’t be 218 signatures for the discharge petition before their big immigration meeting, but other sources aren’t so sure. They argue the GOP leadership won’t get a deal before then causing the holdouts on the discharge petition to sign after the meeting.

“They’ll sign as soon as the conference ends,” said one source knowledgable with the process.

Here are some members who were thought to be in play who tell Fox News they won't sign: House Appropriations Committee Chairman Rodney Frelinghuysen (R-NJ), Rep. Don Bacon (R-NE) and Rep. Dan Donovan (R-NY). All represent swing districts. Frelinghuysen is retiring.

That said, a source closely following the process suggests there are other members to watch, including Reps. Dennis Ross (R-FL), Daniel Newhouse (R-WA) and Walter Jones (R-NC). Ross is upset about how the farm bill imploded. Newhouse has some moderate tendencies. Jones likes to buck leadership.