The race for the Democratic nomination has just passed a critical milestone.

The presidential candidates have been tested in three key parts of the country: the American heartland (Iowa), the North-East (New Hampshire), and now in the racially diverse American West.

The results of the Nevada caucus came in overnight and they confirmed what many suspected.

Senator Bernie Sanders is gathering serious momentum ahead of the next major round of contests.

Hispanics flocked to his banner. He won over union voters, young voters, and black voters.

He is already the clear favourite to win the Democratic nomination and within ten days he may become unstoppable.

Bernie Sanders is winning support from young voters. Credit: AP

That’s pretty remarkable when you stop to think about it. The Democrats are desperate to oust President Trump from the White House.

Many of them believe America’s very future as a functioning liberal democracy depends on it.

And yet they appear likely to choose a 78-year old self-described democratic socialist who is certain to alienate many suburban women, centrist Americans, and independent voters.

The very groups that Democrats will need in November.

But Bernie Sanders has attributes that make him a wildly popular figure among young millennials and party activists.

He has been consistent for decades. He is not talking of gentle, incremental reform. No tinkering for Bernie.

Rather, the Vermont Senator wants a policy revolution - free medical care for all, free college education, a tax on the richest Americans, an end to the fossil fuel industry, a Green New Deal, an economy that is tilted away from Wall Street and that significantly redistributes power and wealth.

That’s routine stuff for the European left. It’s revolutionary talk for America.

And here’s the risk:

The radical Bernie message might work if America faced a Great Recession, an economic crisis, high unemployment, major wars, and falling wages.

But can it work when American employment is at an all-time high and by many barometers the economy is doing exceptionally well, with the stock market soaring?

In other words, will Americans really vote for a revolution when things are going well?

Certainly, Trump appears ecstatic at the prospect of running against Sanders in November.

He is already congratulating the candidate and - with a heavy dose of political provocation - warning Bernie that the Democratic Party establishment won’t tolerate his victory.

Will Bernie Sanders face Donald Trump at the polls? Credit: PA

Next up is South Carolina on Saturday.

That may be Joe Biden’s last stand.

And then in 10 days time we arrive at Super Tuesday - March 3 - when a large number of key states all vote on the same day.

If Sanders does well in those contests he will be marching to the nomination.

But it may fracture the very coalition of voters that Democrats require if they want to win the White House.

It is difficult seeing Bernie pivoting towards the middle ground.

After all, his primary appeal is his very consistency.

He is a radical candidate promising major structural change to America, or he is nothing.