Hillary Clinton has won her second endorsement in as many weeks from a member of the Republican foreign policy establishment, with former National Security adviser Brent Scowcroft issuing a statement of support for her presidential campaign.

"She brings truly unique experiences and perspective to the White House," wrote Scowcroft, who served four presidents and co-wrote George H.W. Bush's post-presidency book on foreign policy. "As Secretary of State, Hillary Clinton helped broker a ceasefire between Israel and Hamas, assembled a global coalition to impose a sanctions regime on Iran, and played a crucial role in persuading Iran to accept limits on its nuclear program."

Scowcroft's endorsement came just six days after Richard Armitage, a veteran of the Reagan and George W. Bush administrations, told Politico he would support Clinton.

"If Donald Trump is the nominee, I would vote for Hillary Clinton,” Armitage told reporter Michael Crowley. “He doesn't appear to be a Republican, he doesn't appear to want to learn about issues. So, I’m going to vote for Mrs. Clinton.”

By contrast, Scowcroft did not mention Trump at all in his seven-paragraph statement. He went further than even some Clinton surrogates have in arguing that she was equipped to make sound national security decisions. "She appreciates that it is essential to maintain our strong military advantage, but that force must only be used as a last resort," he said.

Strikingly, Scowcroft did not refer to Clinton's support for the 2003 Iraq War, which he opposed.

No elected Republicans have endorsed Clinton, but Trump's takeover of the party has earned her a second look from some donors and foreign policy brahmins. The effective end of Sen. Bernie Sanders's campaign against Clinton has also removed one of the last impediments for those Republicans who want to get behind her, if only for one election.

Scowcroft sent out the signed statement to an email list of friends and associates on Wednesday morning. He stated his intention to vote for Clinton but did not urge other Republicans to do the same.

Anne Gearan contributed reporting.