The Democrats have wrapped their fourth round of debates. Here are some key takeaways:

— Warren was a target. The candidates really wanted a split-screen moment with Elizabeth Warren -- and spent almost no time attacking former Vice President Joe Biden. It was a sign of her momentum in the primary in recent months that the candidates are beginning to see more political benefit to striking contrast with the Massachusetts senator. Amy Klobuchar, Pete Buttigieg and Mr. Biden knocked her consistently; Andrew Yang and Kamala Harris sought more targeted digs regarding breaking up Big Tech and whether Twitter should suspend President Trump's Twitter account, respectively. This was one of the biggest themes throughout the night.

— Hunter Biden not a focus. The Democrats continued to sidestep all questions about whether it was appropriate that Mr. Biden's son, Hunter, held a position on a Ukrainian company's board while his father was vice president. Sen. Cory Booker knocked moderators for asking candidates whetherthey thought it was an improper relationship. "We are literally using Donald Trump's lies...and attacking a stateman. That was so offensive," Mr. Booker said. "The only person sitting at home that was enjoying that was Donald Trump." Meanwhile, all the Democrats on stage support the House impeachment inquiry.

— A big topic went undiscussed. After a heavy focus on immigration in prior debates, the subject was barely mentioned tonight save for one passing note from Julian Castro. While discussing President Trump’s pullout of troops from the region, the former secretary of Housing and Urban Development under President Obama quipped that Mr. Trump was “caging kids at the border and effectively letting ISIS prisoners go free."

— Warren still elusive on health care.The senator for weeks has faced questions about whether she would raise middle-class taxes to finance Medicare for All, something Sen. Bernie Sanders has said would happen (though he says the tax increase would be more than offset by lower health costs). She continued to dodge on that question, refusing repeatedlyto say yes or no when asked by moderators and her rivals to explain if she'd finance her plan with a middle-class tax hike. "I will not sign a bill into law that does lower costs for middle-class families," she vowed instead. That was a new line for her. It'll be interesting to see how it plays on the campaign trail if she incorporates it into her stump speech.

— Democrats' favorite Republican. Three candidates named the late Sen. John McCain when asked to name a "surprising" person with whom they had a valued relationship. It further cemented Mr. McCain as a hero to many Democrats as Mr. Trump has critiqued him — even after his death last year.

That's it for us tonight As always, thanks for reading!

— Joshua Jamerson