As congressional Democrats dramatically scale back the most ambitious social spending bill since the 1960s, they’re placing much of the blame on moderates who have demanded changes.

One senator, Kyrsten Sinema of Arizona, has played an outsized role in shaping the bill — but has remained quiet about why. Today, we explore what brought her to this moment.

Guest: Reid J. Epstein, who covers campaigns and elections for The New York Times.

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Background reading: 

• How Senator Kyrsten Sinema has undergone a political metamorphosis.
• Progressive activists have adopted more aggressive tactics against Ms. Sinema and other centrist holdouts as they have blocked aspects of President Biden’s agenda.

For more information on today’s episode, visit nytimes.com/thedaily. Transcripts of each episode will be made available by the next workday.