Sen. Bernie Sanders‘ 2020 campaign has made major gains since the Vermont senator had a heart attack in early October.

Sanders has surged in polls in early voting states as well as at the national level, and garnered major endorsements along the way.

The self-declared Democratic socialist, 78, could be the most underestimated candidate in the race, coming back even stronger after a health scare that would derail most campaigns.

Visit Business Insider’s homepage for more stories.

Two months after a heart attack, Sen. Bernie Sanders is surging in the polls in early voting states and at the national level, while garnering endorsements from prominent left-wing groups and figures.

From the moment Sanders, 78, launched his 2020 campaign, there has been much speculation about how his age could impact his chances. The heart attack in early October accelerated this conversation. For many candidates, such a health scare could knock them out of the race, but Sanders‘ campaign has proven to be remarkably resilient and the Vermont senator seems to be breathing new life into it.

Sanders gets less media attention that other top-tier candidates like former Vice President Joe Biden and Sen. Elizabeth Warren, according to an analysis from The New York Times. Though some of this is likely due to Biden’s name frequently being referenced in relation to the impeachment inquiry into President Donald Trump, it could also reflect that the media is discounting and perhaps underestimating the Vermont senator.

Shortly after the heart attack, Sanders was endorsed by rising Democratic stars Reps. Alexandria Ocasio-Cortez of New York, Rashida Tlaib of Michigan, and Ilhan Omar of Minnesota – three members of the so-called „Squad.“ Since then, things have generally been looking up for the self-declared democratic socialist.

Sanders is up in the polls at the national level and in early voting states

In a Monmouth University poll of Democrats and Democratic-leaning voters released Tuesday, Sanders (21%) came in second overall behind Biden (26%), with Warren (17%) trailing both of them. Comparatively, Sanders (20%) was trailing Warren (23%) and Biden (23%) in the same poll in November, as well was in late September (Sanders was at 15%, Warren at 28%, and Biden at 25%).

And the latest Morning Consult polling places Sanders in second overall among 2020 Democrats at both the national level and early primary states – ahead of Warren and behind Biden.

Sanders won New Hampshire in a shocking landslide victory in 2016, but it’s open to question as to whether he can pull it off again in 2020. With that said, recent polling in the state that holds the first-in-the-nation primary bodes well for the Vermont senator.

A late November poll in New Hampshire from WHDH 7 News/Emerson College showed Sanders leading the pack with 26%, followed by South Bend Mayor Pete Buttigieg at 22%. That was a huge leap for Sanders from the same poll in September, when he came in at third with 13%, behind Biden (24%) and Warren (21%).

But a more recent New Hampshire poll from WBUR places Sanders in third in the state, with 15% of the state’s likely Democratic primary voters stating they support or lean toward him. The poll suggests a tight race, however, placing Biden slightly ahead of Sanders with 17% and Buttigieg in first with 18%.

Sanders has also made huge gains in Iowa, the site of the first primary contest in early February.

The latest WHDH 7 News/Emerson College Iowa poll, released on Tuesday, showed Biden with a narrow lead over Sanders among Democratic caucus voters: 23% to 22%. This represents an increase of nine percentage points for Sanders from the same poll in October, surging up from 13%. At the same time, Warren’s numbers in Iowa plummeted over the same period, dropping from 23% to 12%.

Since 1972, no candidate has gone on to win a major party nomination without coming in the top two in either Iowa or New Hampshire

Sanders is also doing well in California, the most delegate-rich state that could prove decisive given an earlier primary date (March 3) than in past election cycles. Since September, the Vermont senator has shot up from third overall to the top of the field with the support of 24% of likely Democratic primary voters in the Golden State, according to a survey by the UC Berkeley Institute of Governmental Studies.

Sanders just nabbed a major progressive endorsement

Though Warren in September held a commanding lead in California of 29% over Sanders (19%) and Biden (20%), she’s dropped down to 22% in the latest poll. Meanwhile, Biden has dropped to 14%.

As he rises in the polls, Sanders has also nabbed a vital endorsement that shows the progressive wing of the party is lining up behind him, even as Warren poses stiff competition in that regard.

The Center for Popular Democracy Action, a coalition of more than 40 progressive community groups with a combined total of about 600,000 members, endorsed Sanders this week.

„Bernie Sanders is the powerful movement candidate we need to defeat Donald Trump,“ Jennifer Epps-Addison, co-executive director of the Center for Popular Democracy Action, said in a statement.

Epps-Addison added: „From ending mass incarceration and deportations to the $15 minimum wage and Medicare for All, Sanders is working hand-in-hand with our communities to champion the policies that we need to thrive.“

Read more:

Trump has implemented much of his conservative agenda through executive power – and it could be easily undone if a Democrat wins in 2020

Trump has implemented much of his conservative agenda through executive power – and it could be easily undone if a Democrat wins in 2020

The 2020 Democratic field is slowly narrowing. Elizabeth Warren supporters tell us why they think she can go the distance.