As moderate and progressive Democrats negotiate where to cut down a broad $3.5 trillion bill containing most of President Biden's domestic priorities, he is talking more and more about incremental progress.

"My objective is to get everything that I campaigned on passed, eventually. It won't all happen at once," Biden told reporters this week during a trip to Michigan, making the argument that temporary new benefits and tax breaks would likely become permanent, if they gain popularity with voters over time.

But Biden doesn't have that same luxury when it comes to one central aspect of his Build Back Better plan: policies aimed at drastically cutting U.S. greenhouse gas emissions.

That's because when it comes to climate change, Biden is facing two tight deadlines.

One of them is a major international climate summit that begins at the end of the month: the Glasgow, Scotland, follow-up to the 2015 Paris climate summit that cemented the last major international climate agreement.

Biden almost certainly needs to arrive showing other world leaders that after decades of dithering, the U.S. has a real, actionable plan in place to meet the climate goals he's set for the country. Otherwise, other countries may dismiss the administration's plans as something that could be undone by Republicans, or unwound by federal judges.

"To meet the 50% or more reduction in U.S. emissions by 2030, we need action now — this year," said Dan Lashof, the U.S. director for the World Resources Institute, which works on climate policy.

Biden set that end-of-decade goal earlier this year, to keep pace with promises made in the Paris climate agreement. It's aggressive, but it's what scientists say is needed to hold back the worst-case scenarios of climate change.

Here's Biden's second, more existential deadline

The worldwide goal has long been to keep the planet's warming under 1.5 degrees Celsius. It's getting harder and harder to meet, the world has already heated by a degree, and extreme weather is becoming more extreme.

"There are potential tipping points where you cross a point of no return for the Amazon forest or for the polar ice caps," said Lashof. "We don't know exactly where those tipping points are. That's part of the challenge. So the more we do sooner, the less likely we are to cross those tipping points."

A trillion dollars — or even more — will likely have to come out of the sprawling bill Democrats are trying to pass without Republican votes in a process known as reconciliation, but environmental advocates like Jamal Raad of Evergreen Action are mostly feeling pretty positive the major climate provisions will stay in.

Unlike earlier points where major climate legislation seemed possible, most moderate Democrats are as eager as progressives to enact meaningful reductions in emissions. On top of that, Raad argued, "[Senate Majority] Leader [Chuck] Schumer has made climate a priority. President Biden campaigned and won on bold climate action and has signaled it as a priority in the reconciliation bill."

West Virginia's Manchin is a skeptic of the central proposal

Biden has repeatedly acknowledged that the fate of the bill lies with the two Democratic senators who are still on the fence: West Virginia's Joe Manchin and Arizona's Kyrsten Sinema.

Manchin comes from a state where coal and natural gas loom large. He's expressed skepticism about the reconciliation bill's lynchpin program to lower greenhouse gas emissions: the Clean Electricity Payment Program, also known as the Clean Electricity Plan.

The plan mirrors state-level policies that have been in place for decades: it would require electric utilities to gradually convert from fossil fuels to clean power sources like wind or solar. Utilities that add 4% more clean energy each year would be rewarded with grants. Those that fall short would be hit with fines.

Under the $150 billion proposal, the grants would have to be directed to electricity consumers.

"I am just not for giving public companies who have shareholders public dollars, free, when I know they are going to be very profitable in the end," Manchin recently told reporters, suggesting the grants could be turned into loans instead.

Minnesota Sen. Tina Smith, the Democrat who has led the push to include a clean electricity plan in the final bill, said Manchin's concern misses the point. The grants are aimed at speeding up the transition from fossil fuels to clean energy in what has become a massive, high-stakes race against time.

"Utilities are not struggling to find banks or other lending institutions to loan them money to build out clean power," Smith said. "What they are working hard to do is to add clean power at a fast rate, the rate that we need in order to meet our climate goals, without having utility rates go up for their customers."

Smith says she and Manchin have been in regular contact about his concerns.

Recent analysis from Schumer's office says Smith's proposal would make up the bulk of emission cuts in the reconciliation plan, along with other tax incentives to speed up the shift to clean energy.

At the current funding level, Schumer's office projects the reconciliation bill would get the U.S. within 5% of Biden's end-of-decade goal to cut greenhouse gas emissions.

The more funding gets whittled away, though, the further off that result becomes.