Demonstrations are "feel good" moments that are mostly counterproductive, except the Woman's day march both due to its size and the lack of any violence which made it a strong contrast to the inauguration. However, most are populated by fringe elements who only managed to give Trump a perfect foil.
The way to stop Trump is to follow the Tea Party, grass root organizing, especially in the "border" states.
In American politics, the 35% on the right and the 20% on the left are basically irrelevant, their positions are writ in stone.
It is the 45% in the center, consisting of the few remaining moderate Republicans, Independents and the moderate Democrats who are the key to change.
The reason the pandering strategy backfired on the Democrats is that it alienated the political center.
If you organize around centralist principles, you can start winning elections in states like the Midwest states that have gone Republican, Wisconsin, Michigan, Ohio, Pennsylvania, Iowa (check their Congressional delegations and their state houses), and challenge in states like North Carolina, Florida, Texas, Georgia, Missouri and Arizona. The Republican core are the traditional farm states, the Great Plains (including Wyoming), Utah, Idaho, Indiana, and the southern states, Arkansas, Louisiana, Kentucky, Tennessee, Mississippi, Alabama and SC. These are the states without big cities whose expanding suburbs (like Fairfax in Virginia) that shift the power base away from rural areas.
The problem is the principles of moderation and compromise aren't exciting - but they're the core of good government. If you want bigger government, first you must stress good and efficient government - because who wants more wasteful and intrusive government? So what's needed is a return to traditional Progressivism, the combination of elitist expertise and populist goals. This means avoiding "big government" in favor of incentive government - i.e. avoid overregulation, paternalism and bureaucracy in favor of a well measured incremental approach that is driven by humility (we can't fix the world, but we can make it better, and we must be open to criticism so we remained evidence based instead of relying on wishful thinking. Not do "what's right" no matter the cost, but "what works"). The Left has never accepted that "the best is the enemy of the good," and sabotages Progressivism in the name of moral certainty.
We are never going to be Sweden, we can become more like Germany - but both countries implicitly depend on a Protestant work ethic that supports a social contract - it is where that ethic has declined or doesn't exist (Greece, Italy, Spain) that bad government and poorly performing business co-exist. So a moderate movement must support traditional values such as hard work, thrift and responsibility in conjunction with a safety net, recognizing that both effort and luck play a role in outcomes, and that providing opportunity is as important as providing a safety net.
The problem is I don't think the Democrats have a leader who can articulate and sell this vision.