Left/Right is not an economic spectrum as much as people want to claim it is, it is a human rights spectrum, and as a result, each side supports different economic views to support or oppose human rights. And Truman nuked Japan. I do not doubt Trump would not jump at the chance to nuke anything or anyone, but Truman actually did.
Left and right are descriptive terms commonly applied to most political diametrics. That includes economics, social politics, etc. That's how they've been understood throughout modern political history, since they came into being to describe French monarchists and revolutionaries.
In terms of taxation, pretty much nobody would dispute that more "progressive" systems-- which place more of the tax burden on higher earners and corporation tax, and/or act in a redistributive way-- are associated with the left. The tax system placed a larger proportion of the burden of tax on the higher earners under Truman, Eisenhower, and Kennedy than it did under Obama.
This is in part, of course, because of their different starting points. Obama inherited a very different Overton Window with regards to tax. But if you're going to be making comparisons between Presidents in vastly different times
anyway, then you cannot simply ignore tax systems have been vastly more progressive in the past.
You can't convince me that this isn't because of pressure from the DNC, it's too stupid of a decision to be made by rational people, and the only people who benefit from it are the DNC.
And I plan on not voting for them.
So you're basing it on an assumption.
An assumption Sanders has been quite explicit in not making (see his statement on the matter), and using that assumption to justify doing the opposite of what Sanders has encouraged voters to do.
...And you believe this is the most effective way of bringing about the kind of politics Sanders represents.
With voters like these, who needs opponents?