What to watch in tonight's Democratic debate

Bernie Sanders is now the clear front-runner for the Democratic presidential nomination, and his opponents are ready to try to knock him down at tonight's debate in Charleston, South Carolina — especially Michael Bloomberg, who was the punching bag at the Las Vegas debate.

Why it matters: This is the last debate before Super Tuesday, when Sanders is expected to win California and Texas and could secure an insurmountable lead for the Democratic nomination. That's a direct threat to the entire field, but especially to Bloomberg, who skipped the early states to focus on the March 3 contests.

• Democrats mostly left Sanders alone in last week's debate so that they could skewer Bloomberg over allegations of racial and sexual discrimination.
• But now his rivals are getting nervous, and they know time is running out.
• Jeb Bush, Marco Rubio and Ben Carson were all on the debate stage in South Carolina during the 2016 Republican primary, and they all dropped out within four weeks.

The state of play: Bloomberg's team released a digital ad yesterday criticizing Sanders' record on gun control and suggesting he is "beholden to the gun lobby."

• "The debate ... needs to be about one candidate and that’s Bernie Sanders," said Dan Kanninen, the Bloomberg campaign’s states director, in a call with reporters yesterday.
• A senior campaign aide told Axios that Bloomberg will draw contrasts with Sanders on guns and health care, but he'll also go after Sanders on electability.
• The former NYC mayor will argue that Sanders is "a down-ballot drag for competitive House races," the aide said, pointing to a polling memo the campaign released today.
• The Bloomberg campaign is expecting Elizabeth Warren to go after him tonight — just like last time — but they don't seem bothered. "The person to beat right now is Bernie Sanders," said the senior aide. "Others will definitely attack him, but what will he gain from going after all of them?"

Sanders and his campaign have labeled Bloomberg an "oligarch," and after Bloomberg's performance in last week's debate, Sanders said that if Bloomberg wins the nomination, "Trump will chew him up and spit him out."

• An NBC News/Marist poll released yesterday shows Sanders and Joe Biden nearly tied in South Carolina, with Tom Steyer in third.

• Last night after a CNN town hall, Sanders released a fact sheet detailing how he would pay for his major plans — addressing what has been one of the main criticisms against him so far.

Biden's team released a digital ad this week citing a report in the Atlantic that Sanders considered a primary challenge to Barack Obama in 2012. Watch for the former vice president to take on Sanders over health care, as he usually does, and electability with a specific focus on his liability for down-ballot Democrats.

• Even Sen. Amy Klobuchar is signaling she's focused on Sanders. A campaign memo yesterday cited "the consequences of having Bernie Sanders lead the top of the ticket, including his divisive politics and health care plan that would kick 149 million Americans off their insurance."
• Pete Buttigieg warned people against nominating Sanders in his speech after the Nevada caucuses, saying he's created an "inflexible ideological revolution that leaves out most Democrats." Watch for him to continue this theme at tonight's debate.

The intrigue: Warren released an ad going negative on Bloomberg today, so she'll likely keep her focus there. But if Warren goes for Sanders, watch for a theme of effectiveness and how much she says she's done for the progressive movement compared to him.