"Can the democrats keep up this momentum for an election cycle!?"
Yeah actually. Easily. That's one of the great things about the timing, the GOP has to scramble to find a message because they can't repeat a lie for a year until it sticks. We only have to keep it up for a few months.
In the meantime:
August: DNC Boost
September: Second Debate Boost (if Trump chickens out this could be a town hall)
October: October Surprise
November: Election
Somewhere in here is the VP pick boost as well.