The Senate voted to advance immigration reform on Tuesday by a vote of 84-15. That means the Senate can now officially start debating the bill, which it will likely vote on by July.

President Obama hailed the vote as a step forward, saying "If you're serious about actually fixing the system, then this is the vehicle to do it." While the bill garnered bipartisan support with 55 Democrats and 27 Republicans voting "yes," it still faces several barriers, mostly from GOP lawmakers. A look at the hurdles to comprehensive immigration reform ahead:

1. The GOP wants big assurances on border security
"If border and national security cannot be guaranteed in this bill, I cannot and will not support it," said Sen. John Cornyn (R-Texas), echoing the top complaint of many Republican senators.

As the bill stands, it commits $4.5 billion to drones, border agents, and increased fencing to bolster border security. The plan is for the U.S. government to monitor 100 percent of the border and stop 90 percent of illegal crossings.

The problem, according to Republicans, is that the legislation merely requires the Department of Homeland Security to have a plan on how to achieve those goals before immigrants could start achieving provisional legal status. Some GOP lawmakers want Congress to confirm those goals have been met before immigrants are allowed to begin their 13-year pathway to citizenship.

But other lawmakers argue that such a change is unnecessary because border security has already shown improvements over the past several years: A recent study found that the number of border crossings has dropped dramatically in recent years due to increased enforcement and the struggling American economy.

2. Some senators also want stricter English requirements
Marco Rubio (R-Fla.), one of the Gang of Eight senators who drafted the bill, isn't happy with its current English requirements. If passed today, the bill would mandate that immigrants applying for legal status demonstrate proficiency in English or prove they are in a language course.

Rubio, the son of Cuban immigrants, doesn't think a language course is enough and wants to change the bill so that undocumented immigrants would have to prove they can read, write, and speak English before applying for a green card.

3. And some are pushing to get would-be citizens to pay all their back-taxes
Sen. Orrin Hatch (R-Utah) wants undocumented immigrants to pay all unpaid taxes before applying for citizenship, a measure supported by Rubio. Critics, however, argue that expecting undocumented immigrants — especially those working in an "underground economy" where they're paid in cash — to calculate and then pay their back taxes all at once is too much to ask.

4. The bill's fate also depends on how much Democrats are willing to compromise
While Democrats certainly have a list of changes they would like added to the bill — including Sen. Patrick Leahy's amendment to allow immigrants to sponsor their same-sex partners for green cards — their main focus will be on how far they're willing to bend to get 60 or even 70 votes in the Senate.

"I want to get as many votes as we can, but not at the expense of the basic agreement," Sen. Dick Durbin (D-Ill.) told Politico. "When some of my friends announce 70 votes, they create an incentive for Republicans to dream up things that they either needed in this bill or outside of it. And we need to temper that."

Even if Democrats can get the votes they need in the Senate, they still have to consider whether the bill will pass the more conservative House, where partisan arguments have stalled progress on its own immigration bill.