Fresh off a series of victories across the US, the Democrats' hard Left are on the cusp of their biggest victory yet.

Abdul El-Sayed, a progressive former health official, is locked in a struggle with Representative Haley Stevens, the establishment pick, to win the party's Senate nomination in Michigan.

It represents a battle for the soul of the Democrats. If Mr El-Sayed claims victory in Michigan, then the hard Left will claim their "crown jewel", according to one strategist.

And if Ms Stevens wins, she can show the party moderates that their faction still has a pulse – if a faint one.

Anti-establishment and anti-Israel candidates have the momentum in the party after sweeping recent primary contests and unseating longstanding incumbents.

On June 23, socialists backed by Zohran Mamdani, the New York mayor and Left-wing kingmaker, surged to wins in the city's congressional primaries.

The victories of the three hard-Left Democrats positioned Mr Mamdani as a figure more in tune with the party than its notional leaders in Congress: Hakeem Jeffries and Chuck Schumer.

A week later, Melat Kiros, a 29-year-old who once called the Oct 7 massacre "inevitable", defeated Representative Diana DeGette of Colorado, who had never faced a serious challenger in her 15 terms in office.

Socialist, it seems, is no longer a dirty word.

According to a CNBC poll of 1,000 registered US voters released on Friday, voters are more likely to support a candidate who labels themselves as a Democratic Socialist than someone who identifies as a Maga supporter.

Donald Trump himself doesn't seem to care. Before last November's New York mayoral election, he attacked Mr Mamdani as a "Communist lunatic". Afterwards, he invited him to the White House and fawned over the "handsome" 34-year-old.

For all of that, Michigan would represent a different magnitude of victory for the hard Left, for several reasons.

First, it is a Senate seat. Progressives have shown they can win a district or a city, but appealing across an entire state represents a much bigger challenge.

True, Graham Platner emerged as a progressive icon in Maine and was crowned as its Democratic Senate candidate. But his opponent, 78-year-old Janet Mills, fought a half-hearted contest, and his campaign later collapsed following a rape allegation – which he denies.

Second, Michigan – unlike Maine – has an open primary system, where anyone can vote in the contests, including registered Republicans and Democrats.

"Michigan is the crown jewel for the Democratic Socialists because it's the proof of concept that they can be competitive in a competitive state instead of just small enclaves like Brooklyn," said Joe DiSano, a Democratic strategist in the state.

"It's enormously consequential for the future of the party," he added.

With more than just a Senate seat at stake, the primary has turned into a vicious contest.

Almost $30m (£22m) has been committed to the race from a campaign group aligned with Apac, the pro-Israel campaign organisation, to help Ms Stevens and hurt Mr El-Sayed, prompting intense controversy.

Mr El-Sayed's supporters, who include Left-wing stalwarts such as Alexandria Ocasio-Cortez and Bernie Sanders, have attacked Ms Stevens for accepting corporate money and claim she is beholden to special interests.

The congresswoman's speeches, in which she appears to have deliberately thickened her accent, have prompted mockery and further claims of inauthenticity online.

Ms Stevens's team, for its part, has painted Mr El-Sayed as someone who will lose the Senate seat in an election in November, wrecking Democrats' hopes of retaking the chamber.

Adverts, funded by the Aipac-aligned United Democracy Project, claim the charismatic former epidemiologist has a "long history of disrespecting women". He has denied the allegations.

Barack Obama, seen as one of the few unifying figures that Democrats have left, has stayed out of it. But his aides are publicly engaging in heated arguments that have prompted claims of a civil war.

Ben Rhodes, Mr Obama's former deputy national security adviser, has criticised Aipac's spending and the "tens of millions in special interest money of all sorts backing Stevens", which he has called "indefensible and terrible".

In turn, Neera Tanden, a former senior adviser in the health department, hit out at Mr Rhodes for failing to mention the "service" of Ms Stevens, who worked for the former president during his first term, to "the country or President Obama".

Even before any of the new breed of progressives enter Congress – if they're elected in November – the party has already been fundamentally reshaped by the hard-Left wave. Under pressure from their grassroots, representatives split 103-98 on blocking military aid to Israel on July 15.

Amid all the factional infighting and scorched earth tactics, there is a risk that Democrats forget about what really matters: the midterm elections in a few months' time.

"It's not just a battle for the soul, but a battle for control of the Senate," said Mr DiSano.

The primary vote on Aug 4, whatever the result, may end up being a pyrrhic victory.

Try full access to The Telegraph free today. Unlock their award-winning website and essential news app, plus useful tools and expert guides for your money, health and holidays.