HELENA — Montana Gov. Steve Bullock said Friday that he uses private email to communicate with staff only about political or campaign-related issues, but he acknowledged the line between politics and state business sometimes gets blurry.

Those blurred lines came to light when Lt. Gov. Angela McLean wrote to Bullock’s private account to express her frustrations about her position weeks before she announced her resignation.

The use of private emails to discuss official business makes it more difficult for citizens, news organizations and others to review them as public records, and private accounts are potentially more vulnerable to hacking. Hillary Clinton, Sarah Palin and Mitt Romney are among the public figures who have faced criticism in recent years for their use of private emails and servers.

Montana doesn’t have a policy on the use of private email by state officials, but Bullock and his staff have never used their private accounts to conceal discussions of state business, the Democratic governor told The Associated Press in an interview.

Government officials are forbidden from using their official email accounts to discuss political or election issues. Bullock and his staff use private email to communicate on those issues, though sometimes government and politics intertwine, he said.

“It’s hard to make a clear line between what is political business and what is state business,” Bullock said. “You want to be somewhat cautious in as much as you can’t use the state email for political or campaign business.”

In an Oct. 2 email McLean sent from her private email account to Bullock’s, the lieutenant governor wrote that she planned to stay in her post regardless of whether Bullock chose her as a running mate in his 2016 re-election campaign. After she told him that, Bullock senior adviser Dave Parker told McLean to imagine her policy initiatives taken away if she stayed in her post, McLean wrote.

That email and a May 28 message seeking a commitment from Bullock that she will be on the re-election ticket were forwarded to McLean’s state email account. They were among hundreds of emails released in public-records requests by news organizations after McLean announced her resignation.

McLean did not respond to a request for comment.

The AP has requested any other private emails between McLean and Bullock that discuss state business, and any that Bullock may have exchanged with others. Andy Huff, Bullock’s chief legal counsel, said the request raises legal issues that must be reviewed.

There is no state law that prevents officials from using private email for official business, but those messages are subject to the same public-records laws as those from a state account, said Helena attorney Mike Meloy, who specializes in freedom of information issues.

A public-records request for a private email can be denied only if the content does not relate to state business, he said. A denial can be challenged in court.