Former U.S. Ambassador to the United Nations John Bolton has officially endorsed Mitt Romney. He announced his decision in favor of the former Massachusetts governor last night on Greta van Susteren’s Fox News show and followed up that announcement today with a formal statement, which was released by the Romney campaign.

Bolton’s reasoning seems to come down to this: Mitt will have to do because nobody better is running. To van Susteren, he said, in reference to himself, “Looking at the whole range of prospective candidates, there was only one candidate who met my test as the ideal conservative, but he decided not to run.”

He then justified his decision to endorse Mitt anyway. “So faced with everyone else, I followed the William F. Buckley Jr. test which is to find the most conservative candidate who is capable of getting elected. There are obviously two variables there. But in the words of that old song, ‘gimme that old time religion, Romney’s conservative enough for me.’”

His formal statement of support for Romney was a little more rousing.

Of all the candidates, Mitt Romney possesses the strongest vision for America’s leadership role in the world, and I am proud to endorse him. … President Obama has sapped America’s credibility abroad, weakened our military and failed to lead on issues vital to U.S. national security. … Mitt Romney will restore our military, repair relations with our closest allies, and ensure that no adversary — including Iran — ever questions American resolve.”

For his part, Mitt Romney is delighted.

In his own statement, Romney called Bolton a “staunch defender of U.S. interests and values” and said he looks forward to consulting with him on ways to restore America’s standing abroad.

In advance of South Carolina, where Romney’s closest competitors are Newt Gingrich and Rick Santorum, this endorsement just underscores the perceived inevitability of a Romney nomination. Gingrich has said, should he become president, he would offer John Bolton the cabinet position of Secretary of State. Bolton’s decision to support someone else shows how likely he thinks it is that Gingrich will win. As for Santorum, the former Pennsylvania senator has articulated a line of thinking on Islamism and Iran that somewhat resembles Bolton’s, so a Bolton endorsement of Santorum wasn’t out of the question. Had Bolton endorsed Santorum, Bolton’s announcement would have mattered more. As it is, this is just another unneeded notch on Romney’s belt, which seems ever more equipped to secure his nomination.