The Senate will take a vote Monday to move forward with legislation to cut off federal funding.
Manchin is the first Senate Democrat to back the legislation.
"It's time they are investigated," Sen. James Inhofe said.
Republicans need 60 votes to move forward with the bill.
Senators are trying to tackle the two issues before leaving Washington.
Nearly every year, a controversy erupts that shakes the political landscape.
Lawmakers kicked the can on a number of political fights until September.
The agency is responsible for "side" agreements with Iran that some lawmakers object to.
Lawmakers want a woman on the $20 bill instead.
The senator is one of nine Republicans who haven't signed on to the defunding legislation.