WASHINGTON — Homeland Security Secretary Kirstjen Nielsen is out. But President Donald Trump’s failures on the border remain.

The number of migrant families at the border is surging.

Trump still doesn’t have his border wall, even though Democrats offered him $25 billion for it in return for the Deferred Action for Childhood Arrivals program being signed into law.

The administration continues to reel from its one-time practice of separating migrant children from their families.

And oh, the longest government shutdown in U.S. history took place due to the president’s insistence on a border wall (which he still doesn’t have).

Trump announced that Kevin McAleenan, the current head of U.S. Customs and Border Protection, will become acting Homeland Security secretary.

The irony of Nielsen’s ouster is that she had been “the most aggressive secretary in the department’s short history in cracking down on immigration,” Vox’s Dara Lind writes. “None of it appears to have been enough for Trump.”

Lind adds, “Nielsen couldn’t make that happen, because no one could, because it’s impossible. The U.S. can’t — even with a wall — physically prevent the entry of unauthorized immigrants onto U.S. soil. And once on U.S. soil, they have certain rights — including the right to request asylum.”

Our colleague, NBC’s Dafna Linzer, makes another point about the massive Department of Homeland Security, which is responsible for much more than immigration and border enforcement: The organization is under serious strain.

Per Linzer: The deputy secretary, Elaine Duke, left one year ago, in April 2018. She was not replaced.

Immigration and Customs Enforcement has an acting head, and his nomination to lead that DHS office was withdrawn, surprisingly, last week.

The Federal Emergency Management Agency, also under DHS, has an acting head.

The inspector general resigned last year and that office is run by an acting head.

And more critically, McAleenan will now leave his post as commissioner of CPB — the largest federal law enforcement agency in the country and under DHS — to become acting DHS secretary.

Tweet of the day

I often come back to this as a defining moment for Trump. He could’ve had the wall and claimed a bipartisan legislative victory (minor, but not nothing) on “chain migration.” Not to mention fix DACA. But he demanded a high price and ended up with nothing.https://t.co/9MkMZ20qJH — Sahil Kapur (@sahilkapur) April 8, 2019

Pete’s Defeat (in 2010)

Maybe no other 2020 presidential candidate has enjoyed a better past month than South Bend, Indiana, Mayor Pete Buttigieg.

But as Democrats look for a nominee who can beat Trump, Buttigieg has to answer this question: How did he lose a statewide race (for Indiana treasurer) to Richard Mourdock by 25 points back in 2010?

Yes, that Richard Mourdock, who lost two years later in a Senate race to Democrat Joe Donnelly after saying that when a woman is impregnated during a rape, “it’s something God intended.”

On “Meet the Press” yesterday, one of us asked Buttigieg about that 25-point loss:

“It was 2010. It's hard for a Democrat to win statewide in the best of years. I was running in the worst of years. But I'm still proud of our campaign,” he said.

There’s no doubt that 2010 was a tough year for Democrats, especially in red states. But it’s also worth noting that Buttigieg underperformed Democratic Senate nominee Brad Ellsworth, who lost to Dan Coats (yes, that Dan Coats) by 15 points.

Of course, the Pete Buttigieg of 2010 isn’t the Pete Buttigieg of 2019 (who just raised $7 million for the quarter); Mourdock was an incumbent in that ’10 race, which is a hurdle for any challenger; and Trump’s election proved that almost anything is possible in our current politics.

But when it comes to electability — at least based on past results — Buttigieg has a more complicated answer to give than, say, Amy Klobuchar (who just won 60 percent in a state Trump almost carried in 2016), or Beto O’Rourke (whose 2.5-point loss in Texas could have been in many other states), or even Elizabeth Warren (who defeated Scott Brown in 2012).

Sanders says he’ll release his taxes “very, very shortly”

In an interview with NBC’s Shaquille Brewster, 2020 Democratic candidate Bernie Sanders said he’ll be releasing his taxes shortly.

But we’ve also heard that one before.

BREWSTER: Taxes, you have filed for the past 10 years. Why not just release them today, (we will) why not just release them today, all of them?

SANDERS: They will be released very, very shortly. April 15th is coming, and we’re gonna do our taxes for this year and that will be the 10th year --

Brewster: But 2016? 2017?

SANDERS: We will-- They will all be there. You’ll be happy to see them. I say when you talk about taxes, President Trump we’re going to release ten years of our taxes, you (meaning Trump) do the same.

[snip]

BREWSTER: With you calling on the president to release his taxes, why not just do it now-- release what you have so far?

SANDERS: We are. Not right this minute.

Brewster: Not today?

SANDERS: We are, not right this minute, you think I have them in my back pocket?

For the record, in the 2016 cycle, Sanders released just one tax return — a summary for 2014. That’s it.

2020 Vision: Booker raised $5 million-plus

On Sunday, Cory Booker’s campaign announced raising more than $5 million for the first fundraising quarter (Jan. 1 to March 31), and that it has more than $6.1 million in the bank — due to Senate money transferred to his presidential account.

To put Booker’s haul into perspective with the other 2020 candidates who have announced their first-quarter totals so far:

Total raised

Bernie Sanders: $18.2 million in 41 days

Kamala Harris: $12 million in 70 days

Beto O’Rourke: $9.4 million in 18 days

Pete Buttigieg: $7 million in 68 days

Cory Booker: $5 million-plus in 59 days

Total raised (average per day)

Beto: $552K

Bernie: $444K

Harris: $171K

Pete: $103K

Booker: $85K+

The candidates have until April 15 to file their first-quarter reports to the Federal Election Commission.

On the campaign trail today

The 2020 Democrats head out west today: Amy Klobuchar and Bernie Sanders speak at a transportation conference in Las Vegas … And Pete Buttigieg also holds two events in Vegas.

Data Download: The number of the day is … 17 percent.

Seventeen percent.

That’s the share of Americans who say they think their taxes will go DOWN as a result of Trump-passed tax reform legislation, according to new numbers released from our NBC News/Wall Street Journal poll.

More Americans think their taxes will go up (28 percent) or stay the same (27 percent.)

Those most likely to think their taxes will go down?

That would be Republicans (33 percent) and higher-income earners (25 percent).

Don’t miss the pod from Friday, when one of us looked at how social media has changed American politics since 2008.

ICYMI: News clips you shouldn’t miss

Mick Mulvaney says that Democrats will “never” see Trump’s tax returns.

What exactly is with Andrew Yang’s universal basic income plan?

Over the weekend, Pete Buttigieg gave an emotional speech about coming out.

POLITICO looks at how Stephen Miller is driving the immigration shakeup.

And RIP Fritz Hollings.

Other news that’s out there…

Trump agenda: I’m all about that base

NBC’s Jonathan Allen takes an in-depth look at Trump’s base-only 2020 strategy.

Trump is looming large over the Israeli elections.

Thousands of families remain separated as a result of the Trump travel ban.

Trump’s 2020 campaign messaging is shaping up to look a lot like his 2016 one.

Dem agenda: War, what is it good for? Absolutely nothing…

The New York Times takes a look at the warring between the DCCC and the progressive wing of the Democratic Party.

The death penalty may be the next frontier for Democratic reformers.

2020: Don’t you (forget about me)

“The Breakfast Club” is becoming a must-stop destination for 2020 candidates.

Bernie Sanders and Beto O’Rourke are recalibrating their strategies after criticism.

O’Rourke’s campaign is strong, but it’s not quite like his Senate race.

Elizabeth Warren is hoping that sweeping policy plans win over voters.

Nielsen’s ouster underscores Trump’s failures on the border