The "almost winning" or "deferred success" is not necessarily a totally failed strategy. By maintaining a only very slim margin between defeat and victory, the Democrats, and particularly liberal Democrats, remain withing striking distance, and by hammering the various successes of the majority as being incomplete or in fact setting up for a horrendous failure somewhere down the road, they keep their base energized.
The unfortunate part of this equation is that the Democrats have no serious alternative solutions, or even suggestions, as to how the situation could be improved, and in those rare occasions when they do gain ascendency, by parliamentary machinations, they mostly keep the same legislative and executive goals, but trumpet loudly that they have been more "successful" in implementing them. Mostly by kicking the can down the road and deferring any significant reform.
They have become the "me-too" party, and have also gained the reputation of "can't do" party as well.
The Democrats have rapidly approached the point of no longer being significant in any endeavor requiring the survival of the United States as a world power. They clearly couldn't handle that responsibility, should it be thrust upon them, and they mistakenly believe everybody else is equally as incompetent.
True, but when it's the best you can do, it kind of sucks as a strategy.