https://www.google.com
and save me a bunch of typing.
He's been an independent for decades so he's not going to get credit for bills in Washington.
Civil rights activist 1960s-70s
Liberty Union party leader 1971-1976 (running for Governor)
Mayor of Burlington 1981-89
Congressman 1991-2007
Senator 2007-present
So he's had about 48 years of political vetting
Too short of a summary:
https://en.wikipedia.org/wiki/Bernie_Sanders
A self-described democratic socialist and progressive, he has advocated for universal and single-payer healthcare and reversing economic inequality. Sanders also supports labor rights, paid parental leave, and tuition-free tertiary education. On foreign policy, he broadly supports reducing military spending, pursuing more diplomacy and international cooperation, and putting greater emphasis on labor rights and environmental concerns when negotiating international trade agreements.
You'll find things like
"Bernie Sanders (I-Vt.) was the most popular senator for the 11th time in a row."
https://morningconsult.com/2019/01/10/americas-most-and-least-popular-senators-q4-2018/
How Bernie Gets Things Done in Congress Without Being Bought Off
https://observer.com/2016/03/how-bernie-gets-things-done-in-congress-without-being-bought-off/
Books he has authored have done reasonably well
https://www.amazon.com/gp/bestsellers/books/5571257011/ref=pd_zg_hrsr_books
He's been advocating for many of his policies for decades.
I think he's influenced the Democratic party to shift some to the left - which I've appreciated because I often like his progressive policies.
That's a start