Former U.S. senator and 1996 presidential candidate Bob Dole was in the Walter Reed National Military Medical Center in Washington, D.C., Tuesday night.

Spokeswoman Marion Watkins told The Associated Press that Dole is in the hospital for a routine procedure and is "doing very well." He is expected to leave the hospital Wednesday.

The 89-year old Kansas Republican's hospitalization was announced by Senate Majority Leader Harry Reid, Democrat of Nevada, on the Senate floor. "He is at Walter Reed, not for a checkup," he said. "He is there because he is infirm. He is sick."

Later, an assistant told CBS News Dole went into the hospital for a "routine" procedure, and could be released as early as Wednesday.

Dole has been admitted to the hospital several times in recent years. He spent nearly a year in Walter Reed in 2010 after complications following knee surgery.

He recently urged the Senate to pass the Convention on the Rights of Persons with Disabilities. Among other things, the proposed United Nations treaty says "discrimination against any person on the basis of disability is a violation of the inherent dignity and worth of the human person."

Some Republicans have objected to the agreement because of its connection with the U.N. debate on the issue that began Tuesday.

Dole lost full use of his right arm and one kidney after he was wounded in World War II. He has long been an advocate for persons with disabilities, and for military veterans.

He was a candidate for vice president in 1976.