Republican running mate Mike Pence, the Indiana governor and former House leader, is the "most conservative" vice presidential nominee of the last 50 years, according to the American Conservative Union's grading system.

The ACU said Monday that Pence has a 99 percent grade, meaning he agrees with or supports the positions of the long-time guard of conservative principles.

By comparison, Democratic running mate Sen. Tim Kaine has the lowest ACU grade in 50 years, zero. That is even lower than populist hero former Sen. Hubert Humphrey, former Vice President Al Gore and even Vice President Joe Biden.

In fact, Kaine is the only nominee with a perfect zero lifetime rating, and he is even lower than President Obama, Sen. Bernie Sanders, and the top of the ticket, Hillary Rodham Clinton. His zero rating comes as the Clinton campaign is trying to portray the Virginia senator and former Democratic Party boss under Obama as a moderate.

The two nominees face off in their only vice presidential debate Tuesday night in Farmville, Va.

The influential ACU runs the annual Conservative Political Action Conference, or CPAC. The next one takes place Feb. 22-25 just outside Washington at its annual home on the Potomac River, the Gaylord Nationa Resort & Convention Center.

Below is the list put out by ACU of the 18 vice presidential nominees going back to Hubert Humphrey in 1965.

Republicans

— Mike Pence, ACU rating 99.0.

— Dick Cheney, 90.8.

— Jack Kemp, 88.8.

— Paul Ryan, 88.6.

— Bob Dole, 82.4.

— Dan Quayle, 80.3.

— Gerald Ford, 64.0.

Democrats

— Lloyd Bentsen 40.5.

— Joe Lieberman, 15.1.

— Al Gore, 14.6.

— Tom Eagleton, 12.9.

— Joe Biden, 12.4.

— John Edwards, 12.2.

— Geraldine Ferraro, 8.3.

— Edmund Muskie, 6.4.

— Hubert Humphrey 5.0.

— Walter Mondale 3.7.

— Tim Kaine, 0.

Paul Bedard, the Washington Examiner's "Washington Secrets" columnist, can be contacted at pbedard@washingtonexaminer.com