'THE ROB PORTMAN EFFECT': New Poll Reveals Why There's Been Such A Historic Shift On Gay Marriage Support

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The record levels of support for gay marriage have been ignited by more Americans than ever saying they know a family member or close friend who is gay, according to a new CNN/ORC poll released Monday.

CNN Polling Director Keating Holland dubbed it the "Rob Portman effect" — Portman shifted his stance on same-sex marriage a little more than a week ago because his son came out to him.

The numbers line up with Holland's theory. In a 2007 CNN poll, only 40 percent of respondents said they supported gay marriage. That number has jumped 12 points in the last six years — 53 percent now say they support same-sex marriage.

Similarly, there has been a 12-point uptick in the amount of respondents who say they have a family member or close friend who is gay or lesbian. In 2007, only 45 percent said they did. Now, 57 percent say they do.

"The rise in support for gay marriage is due in part to the rising number of Americans who have become aware that someone close to them is gay," Holland told CNN.

The poll comes a day before the Supreme Court is set to hear a challenge to California's Proposition 8, which bans gay marriage in the state. On Wednesday, the court will hear a challenge to the federal Defense of Marriage Act.

Along with Portman, a number of politicians have come out in support of same-sex marriage in the weeks leading up to the Supreme Court cases. Last week, former Secretary of State Hillary Clinton announced her shift. And over the last 24 hours, Sens. Claire McCaskill (D-Mo.) and Mark Varner (D-Va.) have announced they now favor same-sex marriage.