Why it matters: The departures of Sinema, Sen. Joe Manchin (D-W.Va.) and Sen. Mitt Romney (R-Utah) — three moderates routinely vilified by their own parties — will leave a massive hole for bipartisan deal-making.

• It's hard to look at today's political incentives, with lawmakers more concerned about their primaries than the general election, and conclude that the vacuum will be filled.

Zoom in: Despite her broad unpopularity, Sinema will leave Congress with a virtually unparalleled record as a bipartisan negotiator.

• The freshman senator wielded outsized power as a moderate swing vote, helping to craft bipartisan laws on infrastructure, gun safety, marriage equality and semiconductor manufacturing.