Republicans believe only 18 percent of Americans support gay marriage.

According to a Gallup survey of 1,535 adults released Monday, 63 percent of respondents say the public is opposed to such unions, while 30 percent say the public supports it.

Less than half of Democrats (43%) and independents (30%) believe the public supports marriage equality. And 18 percent of Republicans say the public supports gay nuptials, while 77 percent say the public is opposed.

For roughly two years, polls have found that a majority of Americans support marriage equality. Gallup's poll found 53 percent of respondents support its legalization, while 45 percent remain opposed.

Most respondents (40%) say such unions will have no effect on society, while 39 percent say they will make it worse. Nineteen percent believe that legalizing same-sex marriage will have a positive effect on society, up from 10 percent in 2003.

In releasing its findings, Gallup wrote: “Groups most likely to support gay marriage generally tilt toward the view that it will neither harm nor benefit society. Thus, it appears that a segment of those who support gay marriage don't necessarily do so thinking that such a policy change would be good for society, but rather because they think it will do no harm – a view that goes along with a more libertarian perspective that allows people to do what they want as long as it doesn't hurt other people. Groups that oppose gay marriage, not surprisingly, view it as harmful to society.”