In 1965, Congress passed and President Lyndon B. Johnson signed the Voting Rights Act. Since then, Congress has voted several times to enhance the freedom to vote for all minorities, most often opposed by Republicans.
In June of 2013, the Supreme Court declared that the 40-year-old discrimination that the act was designed to prevent was no longer valid in today’s America and weakened the enforcement portions of the act.
The Republican-controlled states of Texas, Mississippi, North and South Carolina quickly proved that the discrimination was still alive by passing legislation that made it harder for minorities to vote. These laws are being questioned in the courts today. A democratically controlled Congress could take action to restore the effectiveness of the Voting Rights Act, but the Republicans would probably fight against that.
So when Donald Trump asks black Americans, “What do you have to lose?” part of the answer is simply, “You stand to lose your voting rights under a Republican-controlled government.”