Republicans in the United States Senate have passed a resolution to fund US Immigration and Customs Enforcement (ICE) and Customs and Border Protection (CBP), the first step in ending a months-long standoff sparked by opposition to US President Donald Trump’s mass deportation drive.

Hours of debate gave way early Thursday to a vote on the resolution, in which Republicans, who hold a slim 53-47 majority in the chamber, used a tactic that allowed them to proceed with a simple majority rather than overcoming a 60-vote threshold.

In the end, 50 Republicans voted in favour, while two broke ranks and joined Democrats in voting against the resolution.

Still, Thursday’s vote was far from the final word on the matter. The Republican-controlled US House of Representatives must pass its own resolution.

Then, committees in the Senate and House must both craft the actual funding legislation, which will be subject to another round of votes.

Trump has said he wants the funding bill on his desk by June 1.

How did we get here?

Condemnation of Trump’s hardline immigration drive crescendoed in January, when two US citizens, Renee Nicole Good and Alex Pretti, were fatally shot by federal agents in Minneapolis, Minnesota.

Democrats, who had been increasingly criticised for inaction during Trump’s second term, derailed pending legislation to fund the US Department of Homeland Security (DHS), which oversees ICE.

Many noted the department and ICE had already received a massive discretionary windfall in a Republican-backed tax bill passed last year.

The move was a risky gambit, forcing the effective shutdown of DHS and leading to several knock-on effects, including Transportation Security Administration (TSA) staffing shortages that snarled airport traffic.

Trump subsequently signed an executive order to pay TSA staff, temporarily alleviating the problem, although officials have warned they face a funding cliff.

Still, Democrats have largely wagered it is more politically toxic to be seen as supporting Trump’s immigration policies, which have become increasingly unpopular among the US public, than to be blamed for the shutdown, which has stretched on for 68 days.

How were Senate Republicans able to pass the resolution?

The Republican resolution effectively allows Senate committees to increase the federal government deficit by about $140bn to fund ICE and Border Patrol. However, top Republican officials have said the final legislation will likely total $70bn to fund both agencies for three and a half years.

Typically in the Senate, the minority party can use a so-called “filibuster” to block legislation. A party needs 60 votes to overcome a filibuster.

With Democrats dug in in their opposition, Republicans are instead pursuing a convoluted process known as a “budget reconciliation”.

Passing funding via reconciliation requires only a simple majority, but it is generally a cumbersome, multi-step process that, among other drawbacks, eats up time that could be used on other legislation.

Under Senate rules, debate on budget resolutions is limited to 50 hours, which lawmakers reached shortly before passing the measure early on Thursday.

What is a ‘vote-a-rama’?

While Republican tactics neutralised Democrats’ ability to filibuster the resolution, the minority party still employed another tactic to both delay the final vote and to force Republicans to take positions on potentially politically fraught issues.

After the 50 hours of debate expired, Democrats conducted a so-called “vote-a-rama”, in which they introduced rapid-fire, often symbolic amendments, which were immediately voted on.

Prior to the early morning manoeuvre, the top Democrat in the Senate, Chuck Schumer, said the party would use the “vote-a-rama” to portray Republicans as out of touch with citizens’ affordability concerns, a key issue ahead of the midterm elections in November.

“This will be a reconciliation of contrasts, and we are relishing that fight,” Schumer said. “Republicans want to shell out billions of dollars to Donald Trump’s private army without any common-sense restraints or reforms. Democrats want to put money in people’s pockets by lowering their costs.”

Three Republicans broke from their party to support an amendment aimed at addressing the high rate of health insurance company delays and denials of claims, underscoring the issue’s salience for those facing punishing re-election campaigns.

Three Republicans also supported an amendment to slash prescription drug prices, introduced by progressive Senator Bernie Sanders.

Meanwhile, Senator John Kennedy, a Republican, sought to lay the groundwork to include the Trump-backed SAVE America Act, which supporters say will increase election security and detractors say will disenfranchise millions of voters, in the final funding legislation.

The push failed, with four Republicans voting against including Kennedy’s amendment.

What comes next?

The resolution passed by Republicans in the Senate is essentially a set of instructions for committees to build the eventual funding legislation. Republicans in the House could seek to change the parameters of those instructions, requiring lawmakers in both chambers to mediate the differences.

Once both sides approve the parameters, the real work of hammering out the final legislation will begin. It will eventually also be subject to another 50-hour debate process, which could then give way to yet another “vote-a-rama”.

Once both chambers pass the final legislation, it will go to US President Donald Trump’s desk for signing. Republicans have said they hope to advance the final legislation by next month.