 He said he was here on behalf of working class Americans. O'Brien did not endorse Donald Trump, and the Teamsters may not formally back any candidate in what would be a blow to Joe Biden, who enjoys union support. Greg Clugston, Milwaukee. There is an added layer of security at the Republicans' gathering. Even before the weekend assassination attempt on Donald Trump, some 4,000 police officers had been scheduled to be here in Milwaukee to provide additional security.