Former Obama strategist David Axelrod claims in his new book that the US President hid his inclinations toward supporting gay marriage during his 2008 campaign. 

In "Believer: My Forty Years in Politics," Axelrod said that Obama was uncomfortable with misleading the public, but wanted to secure the black vote. 

In 1996, the then-senator voiced his support for gay marriage in a questionnaire, indicating "I favour legalising same-sex marriages, and would fight efforts to prohibit such marriages."

When he ran for president, however, he took a different stance. 

"I believe that marriage is the union between a man and a woman," Obama told Rick Warren's Saddleback Church in 2008.

"Now, for me as a Christian — for me — for me as a Christian, it is also a sacred union. God's in the mix."

Axelrod contended that the change was not a shift in opinion on Obama's part, but the result of coaxing from his advisors. 

"Opposition to gay marriage was particularly strong in the black church, and as he ran for higher office, he grudgingly accepted the counsel of more pragmatic folks like me, and modified his position to support civil unions rather than marriage, which he would term a 'sacred union,'" he wrote in "Believer."

The former advisor admitted that differing positions were something Obama was uncomfortable with. 

"Having prided himself on forthrightness, though, Obama never felt comfortable with his compromise and, no doubt, compromised position," Axelrod wrote.

"He routinely stumbled over the question when it came up in debates or interviews."

President Obama is the first sitting US president to publicly support same-sex marriage, and under his administration dozens of states have allowed gay marriage.