Bernie Sanders may have won the Nevada Caucuses, and might go on to win the Presidential nomination of the Democratic Party, but he is a potential threat to Democratic control of the House of Representatives, and the goal of gaining control of the US Senate in 2020 and beyond.
If Sanders hopes to accomplish anything, he needs a Democratic Congress, but his extreme stands on domestic and foreign policy threaten a total destruction of the Democratic Party in the short term.
And if the Democrats cannot keep control of the House and gain the majority in the Senate, then nothing that progressives want will be accomplished, and the judicial branch, already corrupted by Donald Trump, will become so right wing that it will create a constitutional crisis for the future when American becomes majority non white by 2040.
We could have a court system and a Supreme Court that will promote white supremacy and create the conditions for a future civil war, and this is no joke!
Measured change is the only answer, not extreme change, which the American people will not agree to en masse!