All eyes turn to Sinema as Democrats face a week that could transform Biden's presidency

(CNN)Democrats this week have the chance to validate their monopoly on political power in Washington, create a legacy of true significance for President Joe Biden and even boost their hopes in daunting midterm elections in three months.

But first they must push a back-from-the-dead climate and health care initiative through the Senate using their tiny majority, notably by locking in the crucial vote of moderate Arizona Sen. Kyrsten Sinema, who has yet to sign off on a bill that may not save Democrats in November but may at least give them a big new win to run on.

Tensions are, meanwhile, soaring between the parties, especially over a Republican blockade of a bill that would fund health care for veterans sickened by exposure to burn pits during service in America's foreign wars. The move opened up the GOP to accusations of cruelty -- and, for once, Republican leader Mitch McConnell has looked outmaneuvered.

The opening on climate did not exist a week ago. But the stunning deal between Senate Majority Leader Chuck Schumer and holdout moderate West Virginia Sen. Joe Manchin created possibilities most of the party thought were gone. Democrats, who have suffered as Biden's legislative agenda repeatedly stalled, will be desperate to pass the bill this week before a Senate recess slows its momentum.

But there remains at least one huge question mark -- the vote of Sinema, whose support is just as critical as Manchin's in the 50-50 Senate. Like Manchin, she has opposed dismantling the Senate filibuster to pass other Democratic priority bills. She did help remodel Biden's larger Build Back Better bill before Manchin blocked it last year. But now there are questions over whether she will back tax changes affecting private equity investors in the Manchin-Schumer compromise. As the 50th Democrat needed to pass the measure with Vice President Kamala Harris' tie-breaking vote, Sinema has huge leverage to seek changes that threaten the bill's fragile foundation, and she has so far avoided giving her verdict on the deal.

Manchin suggested on CNN's "State of the Union" on Sunday that he hadn't spoken to Sinema about the package since he agreed on it with Schumer. But he paid tribute to his Arizona colleague and her previous work on reducing prescription drugs prices -- a goal that is included in the new draft law.