Richard Grenell, an openly gay foreign policy expert hired by Mitt Romney's presidential campaign, has resigned after only two weeks on the job.

In a statement obtained Tuesday by Jennifer Rubin, a conservative columnist for The Washington Post, Grenell said, "While I welcomed the challenge to confront President Obama's foreign policy failures and weak leadership on the world stage, my ability to speak clearly and forcefully on the issues has been greatly diminished by the hyper-partisan discussion of personal issues that sometimes comes from a presidential campaign."

Grenell also thanked Romney for not making his sexual orientation an issue when he was hired.

The Romney campaign had come under fire in some conservative circles for hiring Grenell. Writing for National Review, Matthew Franck argued that Grenell's staunch pro-gay-marriage advocacy could mean that he would pursue an agenda that elevates gay rights above religious freedom in a future Romney administration.

Grenell was also criticized for using crude language talking about women on his Twitter account. He later apologized and deleted the tweets.

Grenell had previously worked in the President George W. Bush administration for Ambassadors John Negroponte, John Danforth, John Bolton and Zalmay Khalilizad.

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Two months after leaving his United Nations position in 2008, he criticized the Bush administration for not backing a United Nations declaration calling for an end to laws that discriminate against homosexuals.

In a message to Rubin, a Romney campaign spokesperson said, "We are disappointed that Ric decided to resign from the campaign for his own personal reasons. We wanted him to stay because he had superior qualifications for the position he was hired to fill."