What to watch for in tonight's Democratic debate

ATLANTA — Three developments are setting the stage for the fifth Democratic debate: impeachment hearings against President Trump, the release of Elizabeth Warren's Medicare for All plan details and Pete Buttigieg's sudden rocket to the top in Iowa polling.

Why it matters: The previous debates largely tested the resilience of two frontrunners, Joe Biden and Warren, with a focus on health care. Tonight's installment has the potential to shake up those dynamics.

One fun thing: The four moderators of Wednesday's MSNBC-Washington Post debate are all women: Andrea Mitchell, Rachel Maddow, Kristen Welker and Ashley Parker.

The big picture: It's Week 2 of the televised House impeachment hearings — and the public phase has put the matter front and center with more American voters than the initial weeks of closed-door depositions.

• Wednesday's testimony from EU Ambassador Gordon Sondland was among the most explosive.
• Five Democratic senators who will be part of the eventual impeachment trial are on the presidential debate stage tonight — and their ability to campaign may be hampered if and when the process moves to the Senate.
• Biden was the most vulnerable of the Democratic contenders at the start of the impeachment inquiry, given Trump's push to get Ukraine to investigate a company tied to Biden's son Hunter's previous work.
• Instead, the Democrats largely rallied around Biden as the focus has turned to questions about Trump holding up foreign aid in an effort to force an investigation of a political rival.

On health care, Warren will remain a target for her opponents — not just the moderates seeking to preserve the private insurance system, but perhaps Bernie Sanders as well.

• Warren released her own Medicare for All plan between last debate and tonight's event. That opens her up to new scrutiny.
• After she released her initial plan, Warren's campaign unveiled a roadmap detailing exactly how she'd overhaul the health care system in a more incremental way.
• One contrast between Warren's and Sanders' proposals is that Sanders' version would require a single bill to be passed to implement Medicare for All.
• Warren would split the process in two: first, expanding Medicaid and then working to pass legislation to fully transition to Medicare for All.

Part of Biden's message is focused on upholding all that Barack Obama accomplished, but that's especially true when it comes to the Affordable Care Act.

• A senior Biden campaign official said the VP will talk about "building on the progressive wins of the Obama era," including the ACA.
• He'll likely argue that he thinks Warren isn't being honest about raising taxes to pay for her plan, and he'll remind voters how difficult it was to pass the ACA in the first place.

The big question: This is the first debate since polling showed Buttigieg zooming to the top in Iowa; will the moderators and his rivals validate those results by turning more scrutiny on his experience, policy proposals or weak standing with African-American voters?

Don't forget: Neither Deval Patrick nor Michael Bloomberg will be on the stage tonight. Patrick, the former Massachusetts governor, announced his entry into the race too late to qualify. Bloomberg, the former New York mayor, has been taking steps toward a late entry but has not formally made a decision.

Go deeper:

• Behind Pete Buttigieg's Iowa rise
• 2020 presidential election: Track the candidates