Former U.S. President George H.W. Bush urged disgruntled conservatives on Monday to rally around John McCain, calling their criticism of the Republican presidential front-runner "grossly unfair."

"His character was forged in the crucible of war. His commitment to America is beyond any doubt," the 41st U.S. president, joined by his wife Barbara, told a joint news conference with McCain in a Houston airport hangar.

"You know, if you've been around the track you hear these criticisms and I think they are grossly unfair. He's got a ... sound conservative record but he's not above reaching out to the other side," he said.

"So I hear these criticisms and Barbara knows I get a little bit annoyed about them frankly," he said, later dismissing them as "absurd."

During the 2000 Republican presidential primary, Senator John McCain was the target of a whisper campaign implying that he had fathered a black child out of wedlock. (McCain's adopted daughter is a naturally dark-skinned child from Bangladesh). Voters in South Carolina were reportedly asked, "Would you be more likely or less likely to vote for John McCain if you knew that he fathered an illegitimate black child?". McCain would later lose the South Carolina primary, and the nomination, to George W. Bush.

In addition, on the week of the nomination vote, dozens of radio stations were called on the same day asking talk show hosts what they thought of McCain's having fathered a black child out of wedlock.