In remarks he said were likely to get him criticized as a bigot, the Florida Republican told an audience at Catholic University that a strong America is impossible without Americans who hold strong values. Seeming to seek a debate over those values, he criticized liberals who defend abortion rights for women but not protections for "the unborn."
While Rubio has consistently held conservative positions on gay marriage and abortion, his current emphasis appears to be an appeal to social conservatives who have yet to settle on a favoured presidential candidate for 2016.
"Even before this speech is over, I will be attacked as someone who is a hater or a bigot or someone who is anti-gay," Rubio said.
Rubio's remarks on social issues come as he is trying to recover from his failed push for an immigration overhaul, now seen as a political misstep.
Rubio helped write the bipartisan immigration overhaul that passed the Senate but stalled in the House as some Republicans balked. Conservatives grew wary of the measure, and the Republican-led House signalled the comprehensive Senate plan would go nowhere.
Rubio did not include immigration in his speech, which focused on the merits of marriage, raising children in two-parent homes and educating them with values. But a member of the audience did ask Rubio about his immigration legislation's hopes in Congress.
"I just don't see how we ever get the support in Washington any time in the next decade" unless lawmakers are convinced the flow of immigrants coming to the United States across its southern border has stopped, Rubio said. The unfolding crisis along the U.S.-Mexico border gives him little hope, he said.
Rubio's priority seems to be winning back the support of the activists who have clout in picking the GOP presidential nominee. Social conservatives have unquestionable sway in the leadoff Iowa caucuses. Fiscal and libertarian-minded conservatives dominate New Hampshire's primary. In South Carolina, religious issues top voters' priorities.
Rubio has been working to make himself more acceptable to factions within the fractured GOP. His series of policy speeches so far have been as varied as high-tech investments, college affordability and a muscular foreign policy. He has quietly been courting leaders from all corners of the Republican coalition ahead of an expected presidential bid.
While his stance on social issues could be an advantage in early nominating, Rubio is also wrapping himself in rhetoric that could haunt him if he makes it to the general election in November 2016.
Perhaps seeking to blunt that criticism, Rubio acknowledged the United States has a history of discrimination against gays and lesbians. He added that his opponents pose what he called legitimate policy questions and urged a respectful discussion going forward: "Tolerance is also a two-way street."
But he said he could not support such marriages despite a quick-moving shift in public opinion on allowing same-sex couples to marry.
"There is a growing intolerance on this issue," Rubio said of those who back same-sex marriages. "This intolerance in the name of tolerance is hypocrisy."
He also said communities should work to fight abortion and to promote children born to married couples. He said he understands single-parent households — including in his extended family — but said abortion is not the answer.
"There is undeniably another person involved in this as well: the unborn child," Rubio said. "An unborn child should be welcomed into life and protected in law."