In a one-on-one interview with Rachel Maddow on Maddow's self-titled show, Sen. Elizabeth Warren has endorsed former Secretary of State Hillary Clinton for president. And she says she’s excited to have a “fighter” in the position. “I am ready to get in this fight and work my heart out for Hillary Clinton.”

“Hillary Clinton won because she’s been out there, she’s a fighter. [...] She gets back up, and she gets back in the fight. As a Democrat, one of the things that frustrates me most is that we don’t get in the fight.” But after decades of Republican attacks against Clinton? “Nobody says she doesn’t know how to throw a punch.”

On why she didn’t endorse sooner: “I thought that the primary was really important. It was an opportunity for Democrats to show, this is what it means to be a Democrat.”

Her respect for Bernie Sanders and his accomplishments remains: “What Bernie Sanders did was powerfully important.” Sanders “brought millions of people into the political process.”

But if Republicans win? “Say goodbye to the Affordable Care Act. [...] Say good by to a Supreme Court that is open and balanced to the American people.”

On Donald Trump: He is “a genuine threat to this country”, and “a threat to who we are as a people.” An “insecure money grubber” who “doesn’t care who gets hurt.”

Warren remained publicly neutral throughout the Democratic race, but after Clinton's delegate wins on Tuesday gave the Sanders campaign no plausible remaining path forward, Democrats have sought to close ranks quickly around the now-presumptive nominee. Her endorsement follows on the heels of the just-released endorsement from the sitting president himself.

Discussions over when the endorsement would happen have been going on for at least the past few weeks, according to multiple sources with knowledge of the process. Some in Warren circles advocated for holding off and giving Bernie Sanders supporters more breathing room after Tuesday night. But endorsing on Thursday was moved up after Obama decided to back Clinton, those sources said.

Warren's own deceptively simple but scathing attacks against Trump and the party that enabled his rise are a reminder of why the Democratic base has so embraced her. Like the equally refreshing-to-listen-to Sen. Al Franken, she entered politics with no particular desire to respect the well-heeled asininities of her new peers. And not only is Warren a true expert on the American financial markets and their regulation, her ability to explain those regulations and, most conspicuously, identify precisely how they are manipulated by the regulated make her one of the nation's top Wall Street watchdogs.

She would be an effective surrogate during any presidential election, but against Donald Trump? Now that's something to look forward to.