WASHINGTON (NEXSTAR) — President Joe Biden arrived in Glasgow, Scotland, Monday for a highly anticipated United Nations summit on climate change, promising bold action from the U.S. even as his climate initiatives are stalled in Congress.

“Glasgow must be the kick-off of a decade of ambition,” Biden told other world leaders. “We’re standing at an inflection point in world history … and this is a moral imperative.”

The White House insists the U.S. will be able to meet promises made to global allies and slash emissions in half by the end of the decade, but the vehicle to do that — the massive Build Back Better social spending plan — still has an uncertain future.

Moderate Democrat Sen. Joe Manchin of West Virginia held a last-minute press conference Monday to say he was not ready to back the package.

“I will not support a bill that is this consequential without thoroughly understanding the impact,” he said. “We must allow time for complete transparency and analysis on the impact changes to our tax code in energy and climate policies.”

He also pressured progressive Democrats to allow a vote on the bipartisan traditional infrastructure bill this week.

“Holding this bill hostage is not going to work,” he said.

The White House later released a statement saying it “remained confident that the plan will gain Senator Manchin’s support.”

Manchin’s vote is key in getting the package passed. It remains unclear if progressives who are calling for even more spending will bend to his demands. The chairwoman of the Progressive Caucus said she’ll leave dealing with Manchin to Biden.

Republicans remain opposed to Biden’s climate goals and the Build Back Better package, which Democrats have pitched as spending on social infrastructure.

“We need to focus on regaining America’s energy independence,” Rep. John Joyce, R-Pa., said. “Passing the green new deal dressed up as infrastructure legislation is not the answer to the problem that we are currently facing.”

Speaker of the House Nancy Pelosi, D-Calif., said she would like to see a vote on the Build Back Better and traditional infrastructure plans this week.