A democracy is nothing more than mob rule, where 51 percent of the people may take away the rights of the other 49.
That's not how the us government works.
The president isn't chosen by popular vote, and presidents have lost the popular vote and still won the election. Representatives and senators are voted in by localities and represent the interests of the individual states they serve (not 51% of the country).
51% of the votes in this country gets you nothing.
That's a false argument. Maybe it would be better to say democracy in the US is tyranny of 70% against the 30% (70% of the votes basically guarantees that you'll win in any US election, period).