I don't agree with your characterization. In his time as a Representative, he basically accomplished nothing notable. He got a lot of amendments passed that were either tiny amounts of money (in terms of federal spending) or common sense bipartisan issues (child labor). In his time as a Senator, he has continued that while also accomplishing two notable items (veterans and federal reserve bills). But both of those started as Republican ideas that he took on developing and getting Democracts on board. He should be looked at favourably for doing all of this.

However, every significant bill he has tried to introduce in either chamber has failed to gain any traction. In particular, failing at gaining bipartisan support. Why is that important? Because those are the issues that he is campaigning on. He isn't campaigning on passing child labor laws and he isn't campaigning on spending $22 million. He is campaigning on massive tax & spend proposals that will fundamentally change the extent to which the federal government engages in (current) private market areas.

Why is the distinction between his amendment record and his campaigning important? Because child labor amendments are not in any way indicative of his ability to get an absolutely anti-tax Republican Party to agree to massive tax & spend, or funding community college, or really any of his proposals. On his campaign's issues, the Republican Party and Bernie Sanders are polar opposites.

Sanders' only hope for being able to pass any of his promises is to have Democratic control of both chambers of Congress, including a super-majority in the Senate, with moderate Democrats then being willing to sacrifice re-election in order to get his progressive bills passed. That's ... a lot to hope for.