The Note: 2020 race already open to disruptions The 2020 race looms. But that doesn’t mean it’s standing still.

The TAKE with Rick Klein

The 2020 race looms. But that doesn't mean it's standing still.

Fresh reminders are being served almost daily about how much can and will change before most candidates even reach the starting line.

A federal judge's ruling could place health care -- yes, again -- as a top issue. That means new standards and new pressures for aspiring Democratic candidates, even as President Donald Trump and his party grapple with realities they didn't really prepare for.

Monday brought the first Senate retirement announcement of the 2020 cycle. The seat being vacated by Sen. Lamar Alexander, R-Tenn., is unlikely to offer a major pickup opportunity for Democrats, but an open primary that could center on loyalty to Trump could shape the presidential race.

Already this week, Tulsi Gabbard and Pete Buttigieg, two potential candidates who won't even be 40 on Election Day, have made headlines with steps perceived as moving them toward presidential runs. They're longshots, but can't be dismissed as tiers of candidates are forming. They look different than they would have six months ago -- and may matter little for how things will stand six months from now.

The RUNDOWN with MaryAlice Parks

The president calls it a "witch hunt" and Republicans like to say nothing has come of it, but reports prepared for the Senate Intelligence Committee this week, further detailing the extent and sophistication of the Russian campaign to inflame racial tensions in the United States, offered a poignant reminder of the purpose of special counsel Robert Mueller's investigation.

African-American communities, in particular, were reportedly the focus of many manipulative, fake accounts in 2016, according to the new reports. The reports also concluded the foreign influence operations have increased "substantially" since the presidential election.

The special counsel's team has charged 13 Russian foreign nationals with conspiring to interfere in the U.S. presidential election and a handful of Americans for lying to investigators about their interactions with Russians.

For example, on Tuesday, the president's former national security adviser Michael Flynn is scheduled to face sentencing for lying to law enforcement agents about communications with the former Russian ambassador to the United States.

Still, the president seems disinterested in the subversive and targeted work by Russians to sow discord here in the U.S. Over the weekend, he referred to his former personal lawyer Michael Cohen, who is cooperating with Mueller's work, as a "rat." Former FBI Director James Comey said Monday that kind of language about a witness "undermines the rule of law."

The TIP with John Verhovek

Alexander's announcement that he will not seek re-election in 2020, along with fellow Tennessee Sen. Bob Corker's departure from Congress this session, marks a continuing generational shift in the Volunteer State, and has already set off a swift round of speculation about who will battle to fill his shoes.

But Alexander's decision also renews the conversation over where the battle for control of the U.S. Senate will be fought come November 2020, and what other members of the Senate GOP caucus could be heading for the exits.

Of the 21 Republican senators currently up for re-election next cycle, only six have served in the U.S. Senate longer than Alexander: Kansas' Pat Roberts, Kentucky's Mitch McConnell, Maine's Susan Collins, Oklahoma's Jim Inhofe, Texas' John Cornyn -- who was sworn in just a month before Alexander -- and Wyoming's Mike Enzi.

Collins, who has been at or near the center of just about every major political battle on Capitol Hill in the Trump era, remains a top Democratic target in 2020, but don't be surprised to see the political future of the incumbent senators from Kansas, where Democrats unexpectedly took the governor's mansion in 2018, or Texas, where Rep. Beto O'Rourke's candidacy renewed hopes of a shift to the left, to become subject of intense speculation in the coming months.

And don't rule out influencers like Taylor Swift, a Nashville resident, who encouraged her legions of fans to vote blue during the midterms.

THE PLAYLIST

ABC News' "Start Here" Podcast. Tuesday morning's episode features ABC News' Kyra Phillips and Matthew Mosk, who explain why a potential return of the Trump Organization to the Dominican Republic is sparking ethical concerns. http://apple.co/2HPocUL

FiveThirtyEight Politics Podcast. Last week, New Jersey Democrats backed off from a plan that would essentially gerrymander their state in Democrats' favor, while Wisconsin Republicans went ahead with a plan to strip the incoming Democratic governor of some of his powers. The FiveThirtyEight Politics podcast crew discusses why Democrats appear less inclined to play power politics and whether that will change. https://53eig.ht/2R3UmPO

WHAT YOU NEED TO KNOW TODAY

Vice President Mike Pence attends rocket launches that will take place minutes apart at Cape Canaveral Air Force Station.

Secretary of Health and Human Services Alex Azar and Surgeon General Jerome Adams will hold a press conference in Washington at 9:30 a.m. to announce a health advisory on e-cigarettes and address the surge in use among teenagers.

Former national security adviser Michael Flynn's sentencing takes place at the U.S. District Court in Washington at 11 a.m.

President Donald Trump participates in a roundtable on the Federal Commission on School Safety Report at 2:15 p.m. in the White House.

The Note has a new look! Download the ABC News app and select "The Note" as an item of interest to receive the day's sharpest political analysis.

The Note is a daily ABC News feature that highlights the key political moments of the day ahead. Please check back tomorrow for the latest.