No, voters do not decide who makes up the DNC and the GOP. Their donors do. Who you can vote for is already pre-approved by their donors. Secondly, the DNC is an imperialist party, because they all wish to retain the IMF, NATO, capitalism itself, and all that goes into imperialism as the necessary endpoint of late-stage capitalism. The only way to fight against the US Empire is by overthrowing it. As long as capitalism is maintained, so too will imperialism be maintained. You cannot have late-stage capitalism without imperialism, and the democrats can't go against their donor-base, which is where they derive their political power from.