The Democratic Party is indeed a "Big Tent", including the Bernie Sanders contingent, yet National Candidates and Party Platforms are consistently Moderate. Bernie ran for President in 2020, but JB was selected, and before him, Obama and Clinton were Moderate choices with Moderate Platforms...albeit "Progressive" in that they moved the country ahead...for ALL Americans....Health Care (ACA)...Infrastructure...
Mamdani is running for Mayor of NYC, and as I've posted previously, a large majority of all Americans across the country favored his "Policies", when his name and DSP affiliation were not mentioned during poll questioning. Let's see if he wins...and more importantly...how he's able to meet the needs of that great city. If he's successful, then it bears learning from what he did and seeing what might be transferable to other jurisdictions.
If you agree with all the rest of what the author is championing, then relax and register as a Democrat once again.