Axios

Sen. Thad Cochran, a Republican from Mississippi and the chairman of the Senate Appropriations Committee, has announced his intent to resign April 1, citing health reasons. Gov. Phil Bryant will appoint someone to temporarily fill Cochran's seat until Nov. 6, at which point Mississippi will host a special election.

Why it matters: This leaves many speculating that Chris McDaniel will drop his primary challenge against incumbent Sen. Roger Wicker and instead run in November's special election. Mississippi is viewed as an incredibly safe Republican seat — but then again, so was the Alabama seat now occupied by Doug Jones.

President Trump fired off a tweet targeting the Obama administration on Monday, claiming that the decision to investigate the Trump campaign in the months before the 2016 election was motivated by wanting Hillary Clinton to win.

The facts: The FBI opened an investigation into possible collusion between the Trump campaign and Moscow in July 2016, after the DNC announced it was hacked by Russians. About a month later, Obama was informed that Vladimir Putin was directly involved in election meddling, but former administration officials say there were limitations to what they could do. [Go deeper: Trump's question about Obama and Russian meddling — answered]

"Christopher Steele, the Man Behind the Trump Dossier: How the ex-spy tried to warn the world about Trump’s ties to Russia," writes Jane Mayer in The New Yorker.

Key quote: "It’s too early to make a final judgment about how much of Steele’s dossier will be proved wrong, but a number of Steele’s major claims have been backed up by subsequent disclosures."

Top Republicans sound increasingly resigned to losing a special House election in Pennsylvania Trump Country a week from today, after party-affiliated groups spent more than $9 million on a race that should be a "gimme."

It's one of the increasingly bearish signs for the GOP ahead of November's midterms, with mammoth stakes for the West Wing: If Dems take the House and there's a Speaker Pelosi, President Trump faces endless subpoenas and perhaps impeachment proceedings.

"He puts rivals around him intellectually. You have people like Wilbur Ross ... and Gary Cohn. And he puts those two guys in front of him and says, 'OK, fight out tariffs in front of me.' And they fight it out, the media covers the fight, but ultimately the decision is made ... So the drama is there, but that is how the president makes decisions."

Here's the number of candidates who had filed with the FEC by Dec. 31 to run for Congress (House and Senate), via WashPost's Paul Kane.

• 2017: 1,218 Democrats ... 807 Republicans
• 2009: 881 Republicans ... 591 Democrats
• 2001: 392 Republicans ... 368 Democrats

A majority of Americans have little to no faith that the Trump administration will stop foreign governments from interfering in the 2018 midterm elections, according to an Axios-SurveyMonkey poll. Republicans overwhelmingly trust the administration, but independents and Democrats don't, by large margins.

Why it matters: This is a huge issue that could undermine public confidence in the elections — and President Trump and the White House team are going to face constant questions about it between now and November. Try to think of the last election where the public didn't trust the president to prevent foreign meddling.

President Trump let loose at Washington's annual Gridiron Club dinner, a white-tie event that invites journalists to put on musical performances and politicians are encouraged to "singe, don't burn" (the Gridiron's motto).

Trump joked about Vice President Mike Pence, his love of Fox & Friends, Jeff Sessions‘ refusal to recusal and the fact that he’d “kick [Joe Biden’s] ass.”