Tim Ryan Out, Polls at Odds: This Week in the 2020 Race

And then there were 18, which was still larger than the presidential field in any other year.

Here’s a rundown of what happened on the campaign trail this week.

One campaign ends …

Representative Tim Ryan of Ohio ended his presidential bid on Thursday, saying he was proud of his campaign for “giving voice to the forgotten people of our country.”

Mr. Ryan argued when he entered the race in April that he could win back the white, working-class Midwesterners who flipped from Barack Obama to Donald Trump, but his campaign never gained momentum.

… will another follow?

The former housing secretary Julián Castro, in serious danger of not qualifying for next month’s debate, said on Monday that he would end his campaign if he didn’t raise $800,000 by Oct. 31.

“These debates have offered our only guaranteed opportunity to share my vision with the American people,” his campaign wrote in an email to supporters, saying the money would fund outreach in early-voting states to get Mr. Castro the polling results he needs to qualify. “If I can’t make the next debate stage, we cannot sustain a campaign that can make it to Iowa in February.”

A similar gambit worked for Senator Cory Booker of New Jersey, who raised $1.7 million in the last 10 days of September after saying he would drop out otherwise.

Biden will take super PAC help after all

Joseph R. Biden Jr.’s campaign dropped its longstanding opposition to receiving assistance from super PACs on Thursday, opening the door for wealthy supporters to spend unlimited amounts of money to try to lift him in the Democratic primary.

Mr. Biden had explicitly renounced super PAC support for his 2020 run, so the move was a stark reversal and an implicit acknowledgment of his weakened position. He entered October with only $9 million in the bank, far behind his leading rivals.

Faiz Shakir, the campaign manager for Senator Bernie Sanders of Vermont, immediately criticized the flip. And Senator Elizabeth Warren of Massachusetts tweeted that it was “disappointing that any Democratic candidate would reverse course and endorse the use of unlimited contributions from the wealthy to run against fellow Democrats.”

Who’s winning? The polls don’t know

Four polls out this week presented a muddled picture of how the Democratic primary is unfolding.

A pair of national polls, for example, had starkly different results: A CNN survey released Wednesday showed Mr. Biden with a commanding lead of 15 percentage points over Ms. Warren, but a Quinnipiac University poll released Thursday had Ms. Warren seven points ahead of Mr. Biden.

The other two polls, both from early-voting states, showed a tight race in Iowa and Mr. Biden maintaining a comfortable lead in South Carolina — although that lead was smaller than in any other debate-qualifying South Carolina poll this year.

An update on debate qualifications

Senator Amy Klobuchar of Minnesota qualified for the debate next month in Georgia, making her the ninth candidate to do so.

Ms. Klobuchar, who is getting a second look after a strong performance in the October debate, received 3 percent support in the Quinnipiac survey and two others this week, giving her a total of four qualifying polls and securing her spot for Nov. 20.

The Democratic National Committee also released new qualification criteria for the sixth debate, which will be held on Dec. 19 in Los Angeles. Candidates will need 200,000 donors (up from 165,000 for November) and one of the following: 4 percent support in four polls (up from 3 percent) or 6 percent support in two early-state polls (up from 5 percent).

Gabbard won’t seek re-election to Congress

Representative Tulsi Gabbard of Hawaii announced Friday that she would not seek a fifth term in Congress and would instead focus on her presidential campaign.

The announcement is likely to fuel speculation that Ms. Gabbard may be preparing for a third-party race for the White House, a prospect that has unnerved Democrats. She has said repeatedly that she has no such plans.

How Sanders would legalize pot

Mr. Sanders introduced his plan to legalize marijuana, a broad proposal that would also expunge many criminal records, provide money for communities affected by the war on drugs and create an independent clemency board.

He promised to use executive action to declassify marijuana as a controlled substance and then introduce legislation to legalize it. And he said he would create a $10 billion grant program for people to start urban and rural farms and marijuana growing operations.

And finally …

An all-female group of journalists will moderate the Democratic primary debate next month, NBC News said on Wednesday.

Rachel Maddow, who was a moderator at the debate in June, will be joined by the veteran NBC News correspondent Andrea Mitchell and a pair of prominent White House correspondents: Ashley Parker of The Washington Post and Kristen Welker of NBC News.