Republicans are so known for this type of shit that it's actually illegal. I don't know if Trump realizes.

The case began in 1981 when the RNC created a “national ballot security task force” that, among other things, undertook mailing campaigns targeted at black and Latino neighborhoods in New Jersey. If mailers were returned undelivered, party activists put those voters on a list to be challenged if they showed up to cast a ballot. In addition, the party was alleged to have hired off-duty law enforcement officers to “patrol” minority neighborhoods on election day.

The DNC sued the RNC in federal court, alleging its activities violated the Voting Rights Act and were intended to suppress voting among minorities. Rather than fight the charges in a trial, the RNC agreed to a consent decree promising to “refrain from undertaking any ballot security activities … directed toward [election] districts that have a substantial proportion of racial or ethnic minority populations.”

http://articles.latimes.com/2013/jan/14/news/la-pn-supreme-court-rnc-voter-fraud-20130114