Why it matters: Sinema has leverage and knows it. Any possible modification of the Democrat’s climate and deficit-reduction package — such as the elimination of the $14 billion provision for carried interest — could cause the fragile deal to collapse.

Her stance is causing something between anxiety and fear in the Democratic caucus as senators await a verdict on the secret deal announced by Senate Majority Leader Chuck Schumer and Senator Joe Manchin last Thursday.

Leading the news: Sinema has given no assurances to her colleagues that she will vote along party lines in a so-called “vote-a-rama” on the $740 billion bill next week, according to people familiar with the matter .

The a-rama voting process allows lawmakers to offer an unlimited number of amendments, as long as they are deemed German by the Senate member. Senators – and reporters – wait late into the night. Republicans, mad that Democrats have a chance to send a $280 billion antitrust package to China and a massive climate and health care bill to President Biden, will use the a-rama vote to force vulnerable Democrats to take politically difficult votes. They will also try to kill the reconciliation package with poison pills — amendments that make it impossible for Schumer to find 50 votes for final passage.

The intrigue: Not only does Sinema say he’s open to letting Republicans amend the bill, but he’s given no guarantee he’ll support a final amendment that restores the original Schumer-Manchin deal. The big picture: Schumer made a calculated decision to negotiate a package with Manchin in secret. He assumed that all its other members, including Sinema, would compromise and support the deal.

Now his caucus is digesting the details, with Sinema taking a printout of the 725-page bill back to Arizona on Friday for some in-flight perusal. Schumer will find out this week if his gamble to keep Sinema in the dark will pay off.

What we’re watching: While Sinema supported the 15 percent minimum book tax in December, which would raise more than $300 billion, Schumer never bothered to check whether her position has changed given the bleak economic outlook.

Schumer and Manchin also introduced language about taxing carried interest as ordinary income, which would raise about $14 billion, knowing full well that Sinema never agreed to it. This move blindsided Cinema.

The intrigue: While Schumer and Manchin have a well-documented and tumultuous relationship — replete with fence-mending private Italian dinners — Schumer and Sinema don’t engage regularly. Flashback: The Schumer-Sinema relationship took a major blow in February when Schumer refused to endorse Sinema for re-election in 2024 when asked directly by CNN.

She did not attend her party’s Parliamentary Committee meeting on Thursday.

Between the lines: Sinema and Manchin have always agreed that President Biden’s original $3.5 billion Build Back Better plan needed to be cut.

They are also on the same page about the need to act on climate change. If Manchin has been primarily concerned with inflation, her guiding principles have always been economic growth and new jobs in Arizona.

The bottom line: Sinema isn’t too happy with how Schumer pitched her this package. It reserves the right to modify it.

But she also knows that a progressive challenger like Rep. Rueben Gallego is all but guaranteed in 2024 if she’s held responsible for killing the Democrats who have hit hardest on the climate bill in years.

Editor’s note: This edition corrects the date of the caucus meeting.