Sen. Bernie Sanders tore into 2020 rival Michael Bloomberg at a Las Vegas campaign event Saturday, saying the billionaire and former New York mayor is trying to "buy the presidency" by paying millions of dollars in advertising.

Why it matters: Bloomberg has surged in national polling recently, having poured millions of dollars into campaign ads largely targeting Trump. His candidacy has become an obvious foil for Sanders, whose grassroots campaign railing against billionaires and the establishment has vaulted him to front-runner status.

The Trump campaign has invested most of its advertising budget to date on Facebook, testing thousands of versions of ads per day to maximize its spending.

But behind the scenes, a source familiar with the campaign tells Axios, the thinking has shifted: "As everyone can see, we still have strong spending on Facebook, but the percentage of our total media budget [on Facebook] is shrinking."

In the lead-up to the 2018 midterm elections — buoyed by Republican control of both chambers — President Trump viewed campaigning for the House as a lower-tier priority and instead poured his energy into rallying for the Senate.

But after the GOP reckoning in 2018, and experiencing firsthand how damaging a Democratic-led House has been to him, Trump is now personally invested in helping Republicans regain the majority in November, several people familiar with his thinking tell Axios.

Michael Bloomberg is just one poll short of qualifying for Wednesday's Democratic debate.

Why it matters: The debate on Feb. 19 in Las Vegas, just before the Nevada caucus, eliminated the requirement that candidates onstage have a specific number of donors. Bloomberg, who has been self-funding his campaign, could face off against his 2020 competitors next week for the first time.

U.S. District Judge Amy Berman Jackson has requested a Feb. 18 "scheduling" conference call in the Roger Stone case, two days before the former Trump associate is set to be sentenced.

Why it matters: Stone's defense team on Friday filed a sealed motion for a new trial — the second time they've done so — amid allegations of juror bias and a growing controversy over Attorney General Bill Barr's intervention in the case.

Former Vice President Joe Biden said on NBC's "Meet the Press" Sunday that Michael Bloomberg's vast fortune cannot "erase" his record, and that scrutiny of Bloomberg's positions on things like race and policing will ramp up now that he's in the national spotlight.

Why it matters: Biden's polling free fall in the wake of poor performances in Iowa and New Hampshire has coincided with a surge for Bloomberg, who appeals to a similar moderate bloc of the Democratic Party. The billionaire's limitless spending capacity poses an especially stark threat to Biden, who has struggled with fundraising.

President Trump is capitalizing on three years of political, economic and global trends that have exceeded forecasts. He has also benefited from a run of extraordinary good luck.

Why it matters: Trump’s top advisers privately marvel at how he flirts with disaster only to catch a big break, whether it's the Iranians botching their response to his military attack or Democrats embarrassing themselves in Iowa on impeachment eve.

Sen. Amy Klobuchar announced on ABC's "This Week" Sunday that her campaign has raised $12 million online in the nine days since the New Hampshire debate.

Why it matters: That's more than the Minnesota senator raised in the fourth quarter of 2019, which had been her strongest quarter yet. It follows a surprise third-place finish in the New Hampshire primary, where she trounced both Joe Biden and Elizabeth Warren — once believed to be Democratic front-runners.

Bernie Sanders hasn't picked up the voters who are deserting Joe Biden, but he's the clear beneficiary of the former vice president's rapid collapse.

The big picture: Of the top six candidates in the race, Sanders' polling numbers have changed the least over the last few weeks — but Biden's fall has made Sanders the biggest winner, since the moderate vote is now splintered four ways.

House Speaker Nancy Pelosi told CNN in an interview airing Monday that she's "not counting Joe Biden out" following the former vice president's disappointing finishes in the Iowa and New Hampshire Democratic primaries.

What she's saying: "There are still races ahead that are much more representative of the country," Pelosi told CNN's Christiane Amanpour in an interview in Munich, Germany, Saturday. Pelosi also defended tearing up her copy of President Trump's State of the Union address on Feb. 4 amid criticism from Republicans, who said it was a '"breach of decorum." She said she only decided to do so after she read the speech and found its content "terrible."

Go deeper: Poll: Joe Biden loses status as most electable Democrat

The Democratic National Committee released its new rules Saturday for this month's South Carolina presidential debate ahead of the state's Feb. 29 primary.

Why it matters: The Feb. 25 debate in Charleston, South Carolina, is the final one before Super Tuesday on March 3.