According to the WaPo:

Pat Robertson, one of the most influential figures in the social conservative movement, will announce his support for Rudy Giuliani’s presidential bid this morning in Washington, D.C., according to sources familiar with the decision.

Robertson’s support was coveted by several of the leading Republican candidates and provides Giuliani with a major boost as the former New York City mayor seeks to convince social conservatives that, despite his positions on abortion and gay rights, he is an acceptable choice as the GOP nominee.

It also slows any momentum for Mitt Romney within the social conservative movement. Romney had recently secured the backing of conservative stalwarts Paul Weyrich and Bob Jones III — endorsements that seemed to strengthen his bid to become the electable conservative alternative to Giuliani. Romney had made no secret of his desire for Robertson’s endorsement and has to be disappointed this morning.

The Politico is reporting the same:

Giuliani has struggled to win support of social conservatives because of his moderate views on abortion and gay rights. But now he has one of the most resonant imprimaturs with Christian voters.

Sen. Sam Brownback (R-Kan.), meanwhile, plans to announce his surprise endorsement of former Sen. John McCain (R-Ariz.) for president on Wednesday, a campaign official told Politico.

The endorsement is to be announced in Dubuque, Iowa.

The alliance gives McCain — once a front-runner, now struggling — a crucial bridge to social conservatives, an important constituency that has remained suspicious of him despite his opposition to abortion.

If anything, the Robertson endorsement is more significant than the Weyrich endorsement that the Romney camp won earlier in the week. Both endorsements strike me as wiser than the threat to either sit home or support a third party bid if Giuliani is the nominee. I’ve written of my ambivalence about Giuliani, but the prospect of religious conservatives handing the Democrats victory next year by sabotaging the GOP nominee ought not be on the table. Robertson and Weyrich get that, even if they arrive at different places when it comes to endorsing a candidate.

Update (AP): Here’s the announcement.