The Note: Electability arguments set for tests in next Democratic debate Placing the top-polling candidates on one stage means fresh matchups for Dems.

The TAKE with Rick Klein

The thing about arguing about electability is that it only works so long as a candidate can demonstrate that he or she is, well, most electable.

The vagaries of polling put that question on display this week, at a moment when former Vice President Joe Biden's campaign is arguing that his polling lead proves a critical point for Democrats.

Wednesday's polling deadline for debate qualification passed without any new entries, yet with another candidate -- Sen. Kirsten Gillibrand -- exiting the field. The next debate -- scheduled for Sept. 12, on ABC and Univision -- is shaping up to be a one-night affair, with official word to come from the Democratic National Committee on Thursday.

Placing the top 10 candidates in polling together on one stage means fresh matchups for Democrats. Biden and Sen. Elizabeth Warren haven't debated each other yet, and neither have Warren and Sen. Kamala Harris.

It also puts Biden squarely up against his argument that he is the best bet to beat President Donald Trump. The Quinnipiac University poll out Wednesday shows Biden with a 16-point edge nationally over Trump -- but with Warren, Harris, Sen. Bernie Sanders and Mayor Pete Buttigieg leading by between 9 and 12 points, too.

Biden said Wednesday he's looking forward to a portion of the campaign where there will be a "smaller number of people so we can have more of a discussion."

He still has plenty of rivals with much to discuss.

The RUNDOWN with MaryAlice Parks

All politics are local, but that doesn't mean every national strategist and campaign won't try to draw sweeping conclusions from the House race next week.

In fact, it's hard to imagine the rare re-do race in North Carolina's 9th Congressional District will be seen as anything but an early proxy for the status of the general presidential election.

Biden released a statement on Wednesday backing Democrat Dan McCready, who will face off against Republican State Sen. Dan Bishop in the special election Sept. 10. Biden's announcement came shortly before the two squared off in their first, and potentially only, debate in the race, hosted by WBTV/Charlotte Observer. Biden endorsed McCready last May during the midterms too.

Trump is set to hold a rally in the district the day before the special election. He carried the area by 12 points in 2016, but in 2018, when Democrats had serious momentum, the race was neck and neck.

A reminder, this race is being held again this year after local election officials finished a long investigation and determined that there was extensive ballot fraud committed by an operative hired by the previous Republican candidate.

The TIP with Kendall Karson

The resignation of one man is leading to a major shakeup for the 2020 Senate battleground.

After Georgia Sen. Johnny Isakson announced his exit from the U.S. Senate at the end of this year due to health concerns, speculation about which pseudo-celebrity Democrats in the Peach State might run began. Former gubernatorial candidate Stacey Abrams and former congressional candidate Jon Ossoff topped the list of hopefuls who might launch a bid for Isakson's seat or challenge Republican Sen. David Perdue.

While a Democratic official told ABC News earlier this week that there is a possibility of Ossoff jumping into the Georgia race "in the near future," before Isakson announced his resignation, a spokesperson for Abrams distanced her further from a potential Senate bid after the announcement, telling ABC News, "Leader Abrams' focus will not change. While she will not be a candidate herself, she is committed to helping Democratic candidates win both Senate races next year."

Next year, the GOP is defending upwards of 20 seats in a battlefield with few foxholes. But Isakson's resignation could mean even more for Democrats, who need a net gain of four seats to flip the chamber -- and just three if a Democrat wins the presidency. Their path to the majority will now almost certainly run through Georgia, and the open seat could potentially determine the balance of power for the entire chamber in a race that could stretch to January 2021.

THE PLAYLIST

ABC News' "Start Here" podcast. Thursday morning's episode features ABC News' Kyra Phillips and ABC News Political Director Rick Klein, who examine Trump's priorities as Hurricane Dorian passes Puerto Rico on its way toward Florida. Then FiveThirtyEight Editor-In-Chief Nate Silver explains why Georgia could be a crucial state for Democrats hoping to retake the Senate in 2020. http://apple.co/2HPocUL

ABC News' "Powerhouse Politics" podcast. Sen. Chris Murphy, D-Conn., told ABC News Political Director Rick Klein and Deputy Political Director MaryAlice Parks that Trump's performance at the G-7 summit exposed a new reality where other world leaders are increasingly sidelining or ignoring the U.S. He also said that there is less than a 50-50 chance expanded gun background checks will pass. https://apple.co/2Zfz5nD

WHAT YOU NEED TO KNOW TODAY

The deadline for campaigns to submit polling and fundraising paperwork to the DNC for certification to participate in the September debate is 11 a.m. Candidates will be formally certified by the early afternoon.

Trump participates in the launch of the U.S. Space Command in the Oval Office at 4 p.m.

New York City Mayor Bill de Blasio speaks at the 63rd Annual AFL-CIO Constitutional Convention in Las Vegas.

Former Vice President Joe Biden and former Housing and Urban Development Secretary Julián Castro are each campaigning in South Carolina.

Sen. Bernie Sanders, I-Vt., has a town hall on climate change in South Carolina.

Former Rep. Beto O'Rourke tours the International Civil Rights Center and Museum in North Carolina.

Rep. Tulsi Gabbard, D-Hawaii, and former Rep. Joe Sestak, D-Pa., are each campaigning in Iowa.

Sen. Cory Booker, D-N.J., campaigns in Oklahoma.

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The Note is a daily ABC News feature that highlights the day's top stories in politics. Please check back tomorrow for the latest.