Ruth Harkin, the wife of Iowa Sen. Tom Harkin, plans to endorse Hillary Clinton for president, aides to the Democratic candidate said today.

The New York senator was scheduled to campaign in Iowa tonight with former President Bill Clinton.

Mrs. Harkin is a member of the Iowa Board of Regents and an influential Democrat in her own right.

Harkin planned to make the announcement at a rally featuring the Clintons at the Iowa State Fairgrounds in Des Moines today.

Harkin has been a longtime friend of the Clintons and worked in President Clinton’s administration as the director of the Overseas Private Investment Corp.

Sen. Harkin has not yet endorsed anyone for the Iowa caucuses, although four of his Senate colleagues are running, including Sens. Joe Biden of Delaware, Christopher Dodd of Connecticut and Barack Obama of Illinois.

The Clintons planned to attend public rallies and private meetings with Democratic activists in the leadoff caucus state tonight in Des Moines,Tuesday in Iowa City and Davenport and Wednesday in the Mason City area, Waterloo and Cedar Rapids.

The campaign trip is the first by the former president anywhere on behalf of Sen. Clinton, besides private fundraisers.