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Donald Trump has said he would use the US presidency to impose term limits on members of Congress as part of a drive to “drain the swamp” of Washington corruption.

Donald Trump. Photograph: George Frey/Getty Images

Currently, House members can serve an unlimited number of two-year terms, while senators can serve an unlimited number of six-year terms. The Republican candidate told cheering supporters in Grand Junction, Colorado, that he would push for a constitutional amendment.

“Six years for members of the House and 12 years for members of the Senate,” Trump said at the rally in an airplane hangar. “Collusion must and will come to an end. It’s time to sweep the corruption out of Washington.”

Trump on Monday issued a five-point plan for “ethics reform” in government to underline his status as an outsider taking on the political establishment, which he claims Hillary Clinton personifies.

The celebrity billionaire’s pledge came as he warmed up for Wednesday’s third and final presidential debate with Clinton in Las Vegas, needing a convincing performance to change a race that seems to be inexorably slipping away.

Trump also spoke in racially charged terms as he defiantly reiterated his warning about potential voting fraud. He urged his supporters to “watch” cities with big African American populations on election day to prevent a “rigged” election.

“They even want to rig the election at the polling booths,” Trump said. “Take a look at St Louis. Take a look at Philadelphia. Take a look at Chicago. Look. Look. If nothing else, people are gonna be watching on November 8. Watch St Louis. Watch Philadelphia. Watch Chicago.”

The remarks came hours after Barack Obama, himself an African American from Chicago, scolded Trump for making the groundless claims that subvert traditions of American democracy, insisting that he had no evidence.