A good overview from First Read:

1. The battle on the left: In June, Sanders and Warren appeared on different nights, giving each the opportunity to stake out ground on the left. Competitors seemed particularly reluctant to criticize Warren, which allowed her to occupy that space virtually unscathed on the first night of the first debate. But with Sanders losing ground in recent polls — and Warren rising in both polls and fundraising — both may be eager to create some differentiation between their brands when they share a stage.
2. Biden v. Harris, round two: By far, the most memorable exchange of the first debates was Harris’ damaging attack on Biden over bussing and his past comments about segregationists. Biden didn’t seem well-prepared at all for that onslaught in June, but he’ll have to show he’s ready to revisit racial issues when he shares the stage with her again.
3. O’Rourke and Buttigieg face off: Mayor Pete Buttigieg’s monster second quarter fundraising haul proved what we’d already had plenty of anecdotal evidence to show — that the South Bend mayor had replaced O’Rourke as the fresh young (white, male) face in the race with a strong donor base and compelling personal story. The two appeared on different nights in June, but Detroit could be O’Rourke’s last best chance to reclaim some of that status (if he still can.)
4. One new face on the scene: Montana Gov. Steve Bullock will make his debate debut, replacing recent drop-out Eric Swalwell. But his pitch as a middle-of-the-country moderate who can work with Republicans will have competition from plenty of others on the stage who are eager to make a similar argument, including Buttigieg, Klobuchar and Hickenlooper.
5. Night Two candidates probably have an advantage — again: One thing we learned from the first set of debates was that even a candidate who performs well on Night One (i.e. Warren or Castro) gets a maximum of 24 hours of positive coverage before being overshadowed by Night Two’s news. The burden will be on Night One’s contenders in Detroit to break through in a way that keeps them in the spotlight for as long as possible — especially with looming anticipation for Wednesday’s Biden/Harris rematch.

Ron Brownstein: “Trump also faces clear evidence that he may be unable to build a winning coalition with just the voters satisfied with his performance in office. That’s evident even with an economy that’s booming, at least according to measures like the low unemployment rate and the soaring stock market.”

“The latest such evidence comes in a new study released today by Navigator Research… The report examines a group that many analysts in both parties believe could prove to be the key bloc of 2020 swing voters: Americans who say they approve of Trump’s management of the economy, but still disapprove of his overall performance as president. And it shows Trump facing significant headwinds among that potentially critical group, partly because of the divisive language and behavior he’s taken to new heights, or lows, since last weekend.”

“After claiming governorships from Republicans in seven states last year, including in crucial presidential battlegrounds like Wisconsin and Michigan, Democratic governors should have good reason to celebrate,” the New York Times reports.

“But there was as much anxiety as optimism when the governors gathered for their annual fund-raising retreat on Nantucket last weekend and grappled with why a party that won with a pragmatic message in 2018 is now veering sharply to the left.”

“A group of governors are alarmed that their party’s presidential candidates are embracing policies they see as unrealistic and politically risky. And they are especially concerned about proposals that would eliminate private health insurance.”

A new NBC News-Survey Money poll finds Joe Biden leads the Democratic presidential field with 25%, followed by Bernie Sanders at 16%, Elizabeth Warren at 16%, Kamala Harris at 14% and Pete Buttigieg at 8%.

“Unionized campaign organizers working for Sen. Bernie Sanders’s presidential effort are battling with its management, arguing that the compensation and treatment they are receiving does not meet the standards Sanders espouses in his rhetoric,” the Washington Post reports.

“Campaign field hires have demanded an annual salary they say would be equivalent to a $15-an-hour wage, which Sanders for years has said should be the federal minimum. The organizers and other employees supporting them have invoked the senator’s words and principles in making their case to campaign manager Faiz Shakir.”

Joe Biden and Sen. Kamala Harris, who clashed at the first Democratic debate, will face off again on July 31, leaving the ideologically aligned Sen. Bernie Sanders and Sen. Elizabeth Warren to appear together on July 30.

Joining Sanders and Warren on the first night, will be Mayor Pete Buttigieg, former congressman Beto O’Rourke, Sen. Amy Klobuchar, Gov. Steve Bullock, Rep. Tim Ryan, John Hickenlooper, John Delaney, and Marianne Williamson.

The next night, with Biden and Harris will be Julian Castro, entrepreneur Andrew Yang, Sen. Cory Booker, Sen. Kirsten Gillibrand, Mayor Bill DeBlasio, Sen. Michael Bennet, Rep. Tulsi Gabbard, and Gov. Jay Inslee.