Washington, DC (LifeNews.com) -- John McCain has picked up another endorsement from a key pro-life senator, as Oklahoma Sen. Tom Coburn has backed his colleague's bid for the GOP nomination. Coburn, an OBGYN and respected pro-life advocate, will help McCain shore up his weak support among pro-life voters.

McCain is considered pro-life when it comes to the issue of abortion, but he's turned off pro-life voters by only recently coming around to support the reversal of Roe v. Wade and because of his votes to force taxpayers to fund embryonic stem cell research.

Coburn is one of the more outspoken pro-life advocates in the U.S. Senate and he's often been one of just a handful of lawmakers willing to stand up during debates and articulate the pro-life perspective on abortion.

He headed to South Carolina on Wednesday to support McCain and said his colleague can be trusted on pro-life issues.

"Since I came to Congress in 1995, I have met one true reformer – John McCain," Coburn said, according to the Tribune newspaper. "He is guided by strong conservative principles, and committed to doing what he believes is right without concern for political consequence."

“John McCain and I have stood side-by-side on many issues," Coburn said, including "ensuring the sanctity of human life.”

“We hear everybody talking about change, but there’s only been one person who is in the race -- in either party -- who has been about change. Their whole life has been about change," Coburn said, according to MSNBC. "Whether it be for judges, whether it be about protecting innocent life, whether it be about standing on principle, even when it costs you.”

However, some political observers say the endorsement has less to do with McCain's views on pro-life issues and more to do with his strong stand against earmarks and Congressional largesse. Coburn and McCain both take strong positions on Congressional spending.

Coburn's endorsement puts him in line with Sam Brownback, the Kansas senator and former presidential candidate who has also backed McCain and promised the pro-life movement he's truly pro-life.

McCain has come under fire from Rick Santorum, a strongly pro-life former Pennsylvania senator and colleague, who doubts McCain's commitment on pro-life issues.