Elected reps will host congressman who oversees US Postal Service for tour, meeting.
In Tucson interview, he says system is secure, because it involves many honest people.
Republican Party says afternoon speech will focus on millennials, election's importance.
Says he will likely leave his choice of a write-in candidate until the end.
Washington Post's national security reporter in Tucson, discusses international events.
The week saw more money, high-profile visits from the Clinton campaign.
Plus: How Pima County plans to balance land development,species protection.
Compared to the previous, 40% more people said this election is "extremely or very uncivil."
4,000 gather on UA Mall, hear ex-candidate warn of potential 'drift toward oligarchy.'