President Trump could begin a reign of tyranny if a majority of Congress and the Supreme Court went along with it. I think it is possible that Republican congressmen/women would be forced to support Trump tyranny out of fear that openly opposing the President would cause them to lose re-election in their own states and districts, as they are doing now.
However, the remaining obstacle - the Supreme Court - would be harder for Trump to commandeer. The conservative justices would feel less pressure to support him, since they don’t have to be re-elected. However, Trump could force Congress to impeach the justices if they opposed him, which might still pressure them into supporting Trump tyranny.
If such a plan worked, Trump could theoretically turn the country into Nazi Germany. I think the possibility of such a disaster is remote -- let's hope that many Republican congressmen/women will be selfless enough to sacrifice their own political careers for the good of the nation should Trump attempt to restrict basic freedoms, although, so far they have been pretty spineless.
In short, there is a way for Trump to turn the U.S. into a dictatorship. Let's hope he doesn't succeed.