Washington (CNN) The out-of-nowhere upset of Democratic Rep. Joe Crowley in Tuesday's New York primary has stunned the Democratic establishment and shook up the party's likely line of succession to become the next House speaker.

Crowley was ousted from his Queens district by Democratic socialist Alexandria Ocasio-Cortez, a 28-year-old Latina running her first political campaign. She is now likely to be the youngest woman ever elected to the House.

It was the most shocking result of 2018's political season so far, and -- though Democrats have avoided intra-party feuds so far this year -- could signal a restive base as the 2020 presidential primary approaches.

"I'm floored," a senior Democratic House aide told CNN.

Crowley, the No. 4-ranking House Democrat, was widely seen as the likely successor to House Democratic leader Nancy Pelosi. And because Pelosi is likely to have a hard time getting 218 votes to become speaker if Democrats win a narrow majority in November, that could have positioned Crowley to take the speakership against Rep. Steny Hoyer, now the House minority whip.

Two Democrats said the next speaker's job is more unpredictable than ever -- and Hoyer's path to become speaker is far from clear. One Democrat said the jockeying will begin immediately.

"It's clearly a signal that people want to get rid of the old and put in the new," one Democratic House member told CNN.

Until now, there had been few signs of a mounting progressive insurgency. Kara Eastman had defeated former Rep. Brad Ashford in a Nebraska Democratic congressional primary and Democratic socialists had won down-ballot races in Pennsylvania and elsewhere. But progressives declined to challenge the party's sitting senators, and in the most important election of 2017 -- the Virginia governor's race -- Lt. Gov. Ralph Northam defeated his more liberal primary opponent, former Rep. Tom Perriello. Now, Ocasio-Cortez's victory could embolden liberal challengers in both 2018 and 2020.

Crowley quickly conceded and backed Ocasio-Cortez, who said in her victory speech that "what we proved tonight is that sometimes the deep midnight and darkness that it feels in our political environment, that there is still hope for this nation."

President Donald Trump, meanwhile, trolled Crowley, suggesting on Twitter -- wrongly, given the overwhelmingly progressive makeup of New York's 14th District -- that Crowley lost because he was too mean to Trump.

Trump tweeted: "Wow! Big Trump Hater Congressman Joe Crowley, who many expected was going to take Nancy Pelosi's place, just LOST his primary election. In other words, he's out! That is a big one that nobody saw happening. Perhaps he should have been nicer, and more respectful, to his President!"

Trump, meanwhile, had more reasons to celebrate Tuesday night. The two candidates he had endorsed won their primaries, in a show of the influence the President has with GOP voters.

Gov. Henry McMaster's victory against businessman John Warren in the Republican gubernatorial runoff came the day after the President traveled to South Carolina to campaign for him.

McMaster was forced into a head-to-head runoff against Warren after falling short of 50% of the vote in this month's primary.

McMaster got the job because Trump named former Gov. Nikki Haley his ambassador to the United Nations. And McMaster was one of Trump's earliest strong supporters within the party.

Trump told South Carolina supporters that a McMaster loss would be portrayed by the "fake news" as "humiliating" for the President.

"So please get your asses out tomorrow and vote," Trump said.

His victory showed the power of Trump's endorsement with GOP voters. It was the first of two major tests of the President's influence of the night.

Trump's endorsement also paid off Tuesday in New York, where CNN projects Donovan has held off a Republican primary challenge from convicted felon and former Rep. Michael Grimm.

Grimm was elected to the seat he was seeking to reclaim three times before resigning in early 2015 after pleading guilty to tax evasion. Donovan was voted in as his replacement five months later and was bidding for his second full term.

Despite Trump's decision to back Donovan, Grimm cast himself as the more authentic backer of the President's political agenda, highlighting Donovan's votes against the GOP tax cuts and a House bill to repeal Obamacare. But Republicans in the district, which includes Staten Island and parts of Brooklyn, ultimately stuck with his replacement -- whom Trump touted as the safer choice for Republicans in November.

Grimm also sought to make common cause with Trump when discussing his legal troubles, which he's called -- without any evidence -- the rotten fruits of a political hit job commissioned by high-ranking Obama administration officials.

Heading into the primary, Donovan had cause for concern: A Siena College poll found that 54% of GOP primary voters believed Grimm would work better with Trump, despite the President endorsing Donovan.

"There is no one better to represent the people of N.Y. and Staten Island (a place I know very well) than @RepDanDonovan, who is strong on Borders & Crime, loves our Military & our Vets, voted for Tax Cuts and is helping me to Make America Great Again. Dan has my full endorsement!" Trump said on Twitter in late May.

He followed up: "Very importantly, @RepDanDonovan will win for the Republicans in November...and his opponent will not. Remember Alabama. We can't take any chances on losing to a Nancy Pelosi controlled Democrat!"

Donovan will take on Max Rose, a combat veteran who's a member of the Democratic Congressional Campaign Committee's "Red to Blue" list of top-tier challengers.

Colorado, Maryland, Mississippi, Oklahoma, and Utah also held elections Tuesday -- with runoffs in South Carolina and Mississippi and primaries elsewhere.

In Colorado, CNN projects Rep. Jared Polis won a competitive Democratic primary to replace outgoing Gov. John Hickenlooper. Polis held off former state treasurer Cary Kennedy and former state legislator Mike Johnston. If he wins in the fall, Polis would be the first openly gay man elected governor in the US.

Another progressive favorite, 2016 Bernie Sanders ally and former NAACP head Ben Jealous, won the Democratic gubernatorial primary to take on Republican Gov. Larry Hogan in Maryland.

In Utah, 2012 Republican presidential nominee Mitt Romney won the Senate primary and is now poised to cruise to election and become a major voice that could counter Trump in the Senate.