A tentative agreement reached Thursday by a group of 10 senators five Republicans and five Democrats aimed at overhauling the nations infrastructure system as called for by President Joe Biden faces a long road to becoming law.

The group, led by Sen. Kyrsten Sinema (D-Ariz.) and Sen. Rob Portman (R-Ohio), drafted a framework this week totaling about $1 trillion in investments on traditional physical infrastructure projects like roads, bridges, and waterways. The agreement would, according to the senators, be fully paid for and not include any new tax increases a red line for Republicans.

We are discussing our approach with our respective colleagues, and the White House, and remain optimistic that this can lay the groundwork to garner broad support from both parties and meet Americas infrastructure needs, the senators said in a statement.

Notably, the group did not release any details about the agreement or appear in public to tout their work, a sign that it may be even more tentative than they are letting on.

The biggest problem for the bipartisan group is math. You need 60 votes to make law in the Senate, and at the moment, they only have 10 for a general framework. Trying to get more Republicans on board could bleed Democratic support and vice-versa.

Its a challenging path to go down, Sen. Roy Blunt (R-Mo.) told HuffPost. Say if youve got a group of five Republicans and fiive Democrats, it means youve only got five Republicans. And that next five will cost you five Democrats.

Already, some Democratic senators are up in arms about the fact that key investments to fight climate change have fallen out of the bipartisan negotiations. Sen. Ed Markey (D-Mass.), one of the chambers biggest climate hawks, threatened to oppose the deal if it did not include robust measures to address the growing climate threat around the world.

They have a package which is climate denial masquerading as bipartisanship ... No climate, no deal, Markey told MSNBC on Thursday.

The Biden administration, meanwhile, has drawn a red line of its own. The White House opposes indexing the gas tax to inflation or requiring electric vehicles to pay a mileage fee to help pay for infrastructure spending because those steps would violate Bidens pledge not to raise taxes on people making under $400,000, according to a person familiar with their thinking.

The bipartisan Senate group has proposed indexing the federal gas tax, an idea that has support among some top congressional Democrats. They also want to repurpose COVID-19 relief funds that have not yet been spent to help pay for their infrastructure package, which most Democrats oppose. And their proposal would be fully paid for without raising taxes on corporations.

Beyond the thorny issues on financing, the two sides are still far apart on the size of the package. The new Senate deal, while larger than a previous Republican offer, is still $400 billion short of Bidens request of $1 trillion for new spending on infrastructure projects.

The White House has made clear that the bipartisan Senate gang isnt the only game in town, either. Congressional Democrats will soon begin a special budget process known as reconciliation even as the Biden administration continues to seek GOP votes on infrastructure. Reconciliation will allow the party to avoid a filibuster and pass a bill unilaterally on a party-line vote.

Top Democrats are watching the bipartisan talks with skepticism, counting the time they have left to produce an infrastructure bill with the annual summer recess quickly approaching.

I look at the calendar, I see two more weeks in June, three weeks in July and one in August and then were in the middle of September. I mean, zoom. Its gone, Senate Majority Whip Dick Durbin (D-Ill.) told reporters on Thursday.