After the House of Representatives narrowly passed the Build Back Better Act -- including $555 billion in climate change investments -- everyone's eyes turned towards the United States Senate where a 50-50 Democratic majority is now in negotiations to pass what would be the largest climate package in American history. While much of the news coverage has been focused on the votes of two moderate to conservative Democratic Senators, Sen. Kyrsten Sinema (D-AZ) and Sen. Joe Manchin (D-WV,) it's worth taking a closer look at the overall Senate dynamic on climate to understand the factors at play beneath the surface.

Climate Legislative Context...and History

The Build Back Better Act will likely be the Biden Administration's biggest and perhaps only shot at an enormous carbon pollution reduction package to help the US reach the President’s enhanced Nationally Determined Contribution (NDC) pledge to cut America’s carbon emissions by 50-52% by 2030. While the House passed a major climate package in 2009, it died in the Senate. The Senate, where each state has two votes regardless of its population, has long had difficulty passing climate-related measures. The last major bipartisan legislative initiative broke down in 2010 after the rise of the Tea Party, and the issue has only become more polarized since.

The World's Greatest Deliberative Body

Past climate measures, like proposed cap and trade laws, would've required 60 votes in the Senate due to the filibuster rule. Because Build Back Better, like Obamacare or the Trump Tax Cuts, is being passed under a Senate procedure known as "budget reconciliation," only a simple majority is required.

Still, getting there is not easy. The "50-50 Democratic majority" is an oxymoron and the smallest majority since 2001-2002. It is, by definition, a barely workable majority according to the numbers alone. For the Biden Administration to pass anything on their agenda (without any Republican votes), even with every possible Democratic vote, they will still be reliant on Vice President Kamala Harris's casting of a tie-breaking decisive vote.

Looking inside the Senate vote-counting, we might consider these storylines:

1. Where are the GOP Climate Warriors?

Lost in so much of the media focus on Manchin and Sinema (they were even nicknamed Manchema by the press) is an overlooked reality: of 50 Senate Republicans, including many who argue they support climate action, not a single Republican vote appears to be in play on this historic climate package. Is this surprising? Sen. Susan Collins (R-ME) represents a blue state that hasn't voted for a Republican presidential candidate since 1988, was an author of climate legislation as recently as 2010, but so far opposes the Build Back Better legislation and hasn't proposed an approach to pass climate change legislation. Other blue state Republicans -- like Senator Pat Toomey (R-PA), or Ron Johnson (R-WI) -- likewise oppose Build Back Better. And because we can’t count on the votes of red-state, coal-state Democrats like Joe Manchin, it underscores an unavoidable mathematical reality: climate advocates need to elect pro-climate Senators from blue states who will insist on action, regardless of which party controls the Senate. Will any green-leaning Senate Republicans join Democrats in passing the biggest climate package ever?

2. Raising Arizona: Will other issues cause Sen. Sinema to bolt?

Arizona's Senator Sinema has been an enigma in much of the debate over Build Back Better, with pundits and observers unsure of what the magic equation looks like to win Sinema's vote. She's in an unusual position: she's the first Democrat to be elected to the Senate from Arizona since 1988. This is an indication that her state may be trending Democratic, with President Biden the first Democrat to win Arizona in a presidential race since 1996, and a new, more reliably Democratic-tilting seatmate in Sen. Mark Kelly. One thing we know: Sinema says she backs a robust climate package, but has balked at other social spending in Build Back Better.

3. Moving the Mountain State

It is difficult to depend on a vote from West Virginia to pass a climate package, as Sen. Joe Manchin represents America's foremost coal state and is likely the last Democrat to win a seat in Congress from this once-reliably Democratic bastion. Twice, West Virginia voters were Donald Trump's biggest, most dependable backers. Democrats haven't carried the state in presidential races since 1996. There’s no political dividend for Manchin at home, especially if he wants to run for reelection, in backing big climate investments. The hope is that he can market both his political independence and Robert Byrd-like ability to bring home the bacon, while arguing to conservative coal-staters that he won concessions from the left and avoided policies he argues would hurt this state, dependent on extractive industries.

4. The Jolly Green Giants

If the overall size of the Build Back Better package is trimmed back, will climate advocates -- especially Senators Whitehouse, Sanders, and Markey -- be able to successfully defend climate from the chopping block? So far, they've been successful.