Mitt Romney stumped for US Senator Mark Kirk in Chicago.
The former presidential nominee says a Republican Senate could keep the president in check.
"It’s essential that we have a Republican Senate to keep the Senate and keep America from going off the rails," he said.
Both Romney and incumbent Senator Kirk say they won’t vote for Donald Trump.
Kirk says he and Romney share another similarity: both are Republicans who have won in states that tend to favor Democrats.
"If I was a standard Republican, I wouldn’t be with a F-minus record from the NRA," he said.
At the same time, Democratic opponent Tammy Duckworth enlisted the aid of David Letterman to help raise campaign funds.