Former President Bill Clinton speaks onstage at the Annual Freedom Award Benefit at the Waldorf-Astoria hotel on Nov. 6, 2013, in New York City.

A Democrat Clinton Wouldn’t Campaign For

There’s a place President Clinton declined to visit during the 2012 campaign.

Former President Bill Clinton speaks onstage at the Annual Freedom Award Benefit at the Waldorf-Astoria hotel on Nov. 6, 2013, in New York City.

Former President Bill Clinton turned down an invitation to campaign on behalf of Sen. Elizabeth Warren, D-Mass., in 2012.

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It was hard to keep former President Bill Clinton off the campaign trail in 2012.

In addition to requesting an aggressive travel schedule on behalf of President Barack Obama, Clinton also eagerly dove into states with competitive congressional and U.S. Senate contests.

[READ: Clinton Payback in Maryland]

He hit the trail for Sen. Bill Nelson in Florida, then-Rep. Joe Donnelly in Indiana, then-Rep. Tammy Baldwin in Wisconsin, Sen. Sherrod Brown in Ohio, Sen. Amy Klobuchar in Minnesota and former Rep. Shelley Berkley in Nevada. He went to North Dakota twice for now-Sen. Heidi Heitkamp.

But, according to the book “HRC,” there was one candidate he notably stayed away from: Elizabeth Warren.

The only place he was asked to go that he declined to visit was Massachusetts, where Elizabeth Warren, an Obama acolyte, was running for Senate. Bill would offer his support in the form of an e-mail fund-raising solicitation, but he would not appear with Warren, who is often mentioned as a potential progressive rival to Hillary in 2016.

The account does not provide any detail explaining Clinton’s own rationale behind this. The former president also stayed out of Missouri, where Sen. Claire McCaskill was in a tight re-election battle. McCaskill had insulted Clinton during a 2006 Senate debate when she said she wouldn’t let her daughter near the former president. To make things worse in the Clintons’ eyes, she was first female senator to endorse Obama in 2008.

But the revelation in Massachusetts provides a window into the cool relationship between Warren and the Clintons.

[ALSO: What Elizabeth Warren Gets Wrong (and Right) About Student Loans]

Warren has repeatedly said she’s not running for president in 2016, pledging to fill out her six-year Senate term. She even reportedly signed a secret letter drafted by female Senate Democrats encouraging Clinton to run for president.

But just this past weekend Warren took on two potential Republican White House aspirants at a state party dinner in Minnesota.

She confronted Rep. Paul Ryan, R-Wis., about his opposition to extending unemployment insurance and skewered Sen. Ted Cruz, R-Texas, for his obstructionism.

“I sometimes think that if Ted Cruz had been around for the Declaration of Independence, he would’ve tried to repeal it because Jefferson was a Democrat,” Warren zapped. “And don’t even get Ted Cruz started on the Humphrey-Mondale dinner. As we speak, he’s off somewhere strategizing on how to repeal the salad course.”