First Read is your briefing from Meet the Press and the NBC Political Unit on the day's most important political stories and why they matter.

Trump tries to stem disorder with a new chief of staff. Can it work?

WASHINGTON — As unconventional as President Donald Trump is, his move on Friday to replace his chief of staff is what a conventional president might do after suffering a big policy loss and a fresh spate of West Wing infighting.

Of course, what's not conventional is not only how soon into his presidency he's had to shake up his chief of staff and his communications shop, but also how many major staff changes we've already seen in his administration.

The constant churn has become a norm for the candidate who famously promised to "hire the best people." Consider these personnel departures to date:

National Security Adviser Michael Flynn — out after 23 days

White House Communications Director Mike Dubke — out after 86 days

FBI Director James Comey — out after 110 days

White House Press Secretary Sean Spicer — out after 183 days

White House Chief of Staff Reince Priebus — out after 189 days

And that's not to mention Attorney General Jeff Sessions, whose fate continues to hang in the balance.

Former Trump campaign chief Corey Lewandowski told one of us on Sunday that “anybody who thinks they're going to change Donald Trump doesn't know Donald Trump,” advising incoming chief of staff Gen. John Kelly to skip any attempts to modify the president’s style.

The challenge for Kelly, as famous for his discipline as he may be, is that the root of the White House chaos is the nurturing of rivalries and the unpredictability that comes from the president himself.

By the way, Kelly will be sworn in today at 9:30am ET, and he’ll already be faced with two developing crises abroad — Russia’s move to expel hundreds of U.S. diplomats and a new missile threat from North Korea.

Trump's Senate math doesn't add up

Speaking of the president's level of discipline, Trump continued to tweet about the health care bill over the weekend, lambasting GOP Senate leaders for failing to upend the chamber's rules to get the bill passed.

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"Don't give up Republican Senators, the World is watching: Repeal & Replace...and go to 51 votes (nuke option), get Cross State Lines & more," he wrote.

What’s more, White House budget director Mick Mulvaney said on Sunday that the White House’s policy is that the Senate shouldn’t hold a vote on any other issue — even the looming debt ceiling crisis — until it votes again on Obamacare repeal.

It goes without saying that the health care bill that went down last week only got 49 votes, not 59, and it missed the mark for passage under reconciliation rules, not regular filibuster procedure. And Senate Majority Leader Mitch McConnell — along with a bipartisan group of 61 senators, by the way — has been outspoken about keeping the 60-vote legislative filibuster threshold intact.

As we wrote last week, the president can't be faulted for a lack of persistence in the health care fight. But this continued hard sell to the Senate (is there such a thing as a soft sell from Trump at all?) is at best a confusing threat.

As Trump continues to push repeal, some Democrats eye single-payer

Lost somewhat in the shuffle of last week’s health care drama was the fact that, even with 10 Democratic senators up for reelection in states that Trump won, no Democratic votes were never seriously considered to be in play even as the bill’s fate remained uncertain.

In fact, as the president has continued to berate his own party for failing to accomplish its repeal goals, there’s been significant movement within parts of the Democratic Party in quite the opposite direction: towards a government-run health care system.

As NBC’s Alex Seitz-Wald and Benjy Sarlin wrote over the weekend: “As Republicans learned last week, making grand promises to the base on health care is easy — following through on them is not. For now, single-payer is little more than a slogan. Despite that, one thing is for sure, the issue is moving in only one direction for Democrats and it’s gaining steam quickly, including with recent converts in billionaires Warren Buffett and Mark Cuban…

"Support for single-payer has jumped 19 percentage points among Democrats since 2014 — and nine points since January alone — to 52 percent, according to a Pew survey in June. With 85 percent of Democrats and Democratic-leaning independents now saying the federal government has a responsibility to make sure every American has health care, two-thirds of liberals favor single-payer as the means.”

Russia makes its move in response to sanctions

On Sunday, in an aggressive response to American sanctions, Russian president Vladimir Putin announced that the American diplomatic mission in Russia must cut its staff by 755 employees.

The State Department called the move “a regrettable and uncalled-for act,” saying the administration is assessing the announcement’s impact and how America will respond.

As Michael McFaul, former U.S. ambassador to Russia, said on TODAY this morning, Russia’s expulsion of hundreds of personnel is far more dramatic than the Obama administration’s move last year to kick out 35 Russian diplomats in retaliation for the country’s meddling in the U.S. election.

“It’s not symmetric to what we did,” McFaul said. “That’s a drastic cut... It’s going to be much harder to do our business in Russia as a result of this.”

Crowd control for 2020

Yes, it feels way too early to talk about 2020. But with Maryland Rep. John Delaney announcing his plans to seek the Democratic nomination last week, it’s evident even at this early stage that the primary will almost certainly start off as a crowded affair.

Delaney’s announcement comes after more than one flatting profile of Rep. Seth Moulton floated the war veteran as a candidate, too.

Members of the House don’t exactly have a great track record on presidential runs (no congressman has been elected president straight from the House since James Garfield in 1880), but the level of uncertainty in the Era of Trump makes it easy for an ambitious pol to say “why not me?”

Add that to the business and celebrity types who’ve now seen that political experience is no prerequisite for winning a national election, and you’ve got a recipe for a big and unruly presidential field.

And, while united opposition to Trump is somewhat obscuring the big divides within the Democratic Party for now, a big and unruly presidential field is one surefire way to bring them to the forefront.

Trump's Day

Trump participates in the swearing-in of incoming Chief of Staff John Kelly at 9:30 am ET, then leads a Cabinet meeting. He meets with both U.S. Ambassador to Israel David Friedman and Secretary of State Rex Tillerson before presenting the Medal of Honor at 3:00 pm ET.