Manchin is chasing a last-ditch bipartisan energy deal. Here are 4 stumbling blocks that could tank the whole thing.

• Manchin is trying to strike a bipartisan energy deal at a critical moment.
• Plenty of Democrats are skeptical his attempt to find an agreement will amount to much.

Sen. Joe Manchin of West Virginia is at it again.

Late last month, he surprised many in his own party by convening a meeting intended to strike a bipartisan energy agreement. It raised a lot of eyebrows among Democrats since they don't believe Republicans will cut a deal that will tackle the climate emergency at an aggressive scale.

Democrats are trying to mount a last-ditch effort to revive President Joe Biden's stalled economic agenda. But they're in a holding pattern while Manchin's latest bipartisan gamble plays out. They can't advance any slimmed-down climate spending plan without his thumbs-up in the 50-50 Senate.

Here's a look at the stumbling blocks that could derail the entire effort.

What should go into an energy or climate bill

Republicans and Democrats generally disagree on how to assemble a climate bill. Democrats in the House had passed $550 billion in clean energy tax credits as part of the Build Back Better plan before that bill died in the Senate after Manchin refused to support it.

Those tax credits would have transitioned the US away from fossil fuels onto wind and solar power, along with incentivizing the purchase of electric vehicles.

Manchin is on a different wavelength compared to most other Democrats. He's pushed for priorities like fast-tracking the Mountain Valley gas pipeline that would cross his state, overhauling the oil and gas leasing process in the Gulf of Mexico, and more federal funding for nuclear and carbon capture projects.

The conservative Democrat has also thrown cold water on the electric vehicle tax credits.

"We want to make sure that we have the reliability that fossil [fuels] has given us and can continue to give us as we basically promote and invest in the new technologies and innovation that's going to take us to the next level," Manchin told reporters on Monday.

Republicans tend to favor investments in nuclear energy and unwinding the regulatory process to make it easier to build oil and natural gas pipelines. There's not a lot of overlap between the parties at the moment.

How to pay for it

Last year, Congress approved a $550 billion bipartisan infrastructure deal after months of wrangling. Much of the dispute centered on how to cover the new spending.

Democrats pushed tax increases on the rich, but Republicans took those off the table early on and vigorously defended the 2017 Trump tax law. Negotiations sometimes veered on the edge of collapse due to disagreements on financing the roads-and-bridges law.

Senate Republicans aren't inclined to hike taxes, particularly with the November midterms around the corner. "I think what you gotta look at is it's gonna have to involve some taxes," Sen. Chuck Grassley of Iowa told Insider. "Probably you're going to find it difficult for Republicans to raise taxes."

Manchin acknowledged the obstacle without specifying how to overcome it. "There's a lot of challenges here," he told Insider.

One possibility is a tax on carbon-intensive imports on products like steel from nations with weaker guardrails on emissions. But that could raise issues with the World Trade Organization.

A backdoor Build Back Better bill

Manchin sunk Biden's House-approved social and climate spending package at the end of last year. Talks have been mostly on ice ever since.

Some Democrats like Sen. Tom Carper of Delaware say they can get onboard duplicating last year's two-track approach to ensure a bipartisan energy package and a reconciliation bill travel in tandem. But Democrats would likely try to use a reconciliation bill to salvage the clean-energy tax measures that formed the spine of climate provisions in the defunct House bill. That could turn off the Republicans they need.

"If it becomes a vehicle for them, then it becomes less attractive to us," Sen. Kevin Cramer of North Dakota told reporters on Tuesday.

Not enough GOP support

Any bipartisan deal needs to clinch at least 10 Senate Republicans so it advances past a filibuster in the Senate and eventually reaches Biden's desk. So far, only a handful have been attending the meetings.

Active GOP members include Cramer, Murkowski, Sens. Bill Cassidy of Louisiana and Dan Sullivan of Alaska.

The number of Republicans still doesn't seem firmed up — and Manchin suggested the amount of Republicans could fluctuate. "We haven't set any guidelines," he said on Monday. "The main thing is to have a meeting of the minds first."