Donald Trump's deputy campaign manager, David Bossie, has blamed former President Bill Clinton's “Don't Ask, Don't Tell” military policy for 9/11.

Since 2000, Bossie has served as president and chairman of the conservative group Citizens United. He became Trump's deputy campaign manager last week.

In his 2004 book Intelligence Failure: How Clinton's National Security Policy Set the Stage for 9/11, Bossie argues that Clinton let the terrorist attacks happen by allowing gay men and lesbians to serve in the military and at the CIA.

Clinton replaced the military policy that barred gay men and lesbians from serving in the military with a more nuanced policy that allowed closeted men and women to remain in the armed forces. The policy, known as “Don't Ask, Don't Tell,” was repealed under the Obama administration.

“That Clinton continued to loathe the military was revealed as soon as he took office and attempted to overhaul military policies, such as allowing homosexuals to serve with the new 'don't ask, don't tell' policy,” Bossie wrote.

Bossie added that “serious security-clearance issues and concerns about homosexuals in the intelligence community” are based on “legitimate rationales.”

“Unfortunately, in the Clinton administration, we didn’t see any serious study of the issue. Rather, Clinton’s ideology, and his need to pay back the homosexual community, forced the CIA to change, regardless of the effect on national security. Where will this end? It is hard to say,” he wrote.

Trump for his part has blamed George W. Bush for the September 11 terrorist attacks that killed and injured thousands of Americans.