If I have an IDEA, build a company around it, and FAIL, is that because the IDEA is wrong, or I failed to execute?

Depends.   Both camps have their forces that are ambivalent to the nature of liberty and our Constitution. Wingers on either side are equally dangerous.

Given the sample size of one, there's often no way to tell.

Once again we're down to definitions, something I'm very wary of where modern politics is concerned.

There is no doubt in my mind that the political background across the western world has shifted in the last few decades.  The consequences of this shift are many and wide ranging but can be said to benefit comparatively few people in ways they recognise.

The policies that have done much of the damage are being promoted and advertised (by all sides for one reason or another) as 'liberal', when I do not in fact think they are - at least not in a traditional sense as I understand it.

I have no difficulty in finding policies that would have been viewed as 'mainstream' half a century ago now billed as 'extreme'.  Clearly the policies themselves haven't changed, but the way we talk about them and refer to them has.  For this we have ourselves, the media and the political ambitions of our representatives to blame.

To answer your question directly ex, there may be many reasons for the failure and the responsibility for this may lie distributed across many aspects of society we can do nothing about as individuals.  Not much of an answer I know, but it's the best I can come up with.

In a nutshell - proper, 'old fashioned' leftist-liberal policies haven't been tried and found wanting, they've been found difficult and left untried.

The Manchester capitalists who supported free trade were Liberals. The Tories opposed free trade and supported high taxation. I don't know when exactly the definition of liberal changed. As I understand it, BOTH parties in your country have big problems. Trump won because he was not a professional Republican. What his party do when his supporters all realise that he's a jerk who is totally unsuited to the job is another matter. We Brits have a different problem. Only the Conservatives can get elected, and Labour are not even providing a meaningful opposition. The Conservatives have some terrible policies, nowadays. America has NEVER tried left-wing policies, as most of the world would recognise it. What you guys call left is slightly less right-wing than the Republicans.