There are structural reasons right now that make it impossible for any Democratic president to get a bill passed the Republican congress. House republicans have zero incentive to cooperate with a democratic president and every reason not to. House Republicans are locked into gerrymandered districts that would probably be heavily Republican anyway in the current political alignment. All cooperating with a democratic President on something like financial reform would get a Republican is a likely heavily financed primary challenger.
Still, many people don't vote. Turnout in the last Presidential election was 58 percent. Turnout in the 14 midterms was 40 percent. Sander's argument is that an aggressive platform would increase turnout, which possibly could allow the Democrats to at least do better in the House if not take it. Further, he argues that the mobilization of a campaign should continue after the election to help a party pass its agenda and govern. I'm not completely convinced that will work, but dissmissing the argument as "kids protesting" is reductive and unfair. I actually think that that there might be an argument that such an approach is perhaps the only way to counteract a potentially fatal weakness in America democracy.