Apparently, the left learned nothing with Reagan. They attacked Reagan instead of putting forth better ideas and they ended up with 8 years of Reagan lol.
There was an element on the right who attacked Obama on every little thing but the difference was the Tea Party: the TP was ideas-oriented instead of sheer opposition because the other guy sucked.
The only thing marches will do for the left is to keep their base energized [assuming they can keep it up for at least two years lol]. But they have zero chance of losing their base and they have zero chance of affecting Trump's people with it.
That leaves the middle. The left needs the middle---the last election demonstrated that. To get them, the left will need more than anger, spittle and Russian conspiracy theories. And you have to assume a fair number of the middle wants to at least give Trump a minute to see if he can get some results.
Personally, I think the left is getting close to alienating the middle with their constant hysteria---if they aren't there already.
They need fresh ideas and fresh leaders more than another march.