Republican presidential candidate Rick Santorum suggested Monday that Wisconsin Governor Scott Walker's opposition to gay marriage is undermined by his wife's stance.

Walker on Monday joined the race for the Republican presidential nomination.

“Spouses matter,” Santorum told conservative website the Daily Caller. “When your spouse is not in-sync with you – particularly on cultural issues, moral issues – [you] tend not to be as active on those issues.”

Tonette Walker recently told The Washington Post that she and her two sons were “disappointed” with Walker's response to the recent Supreme Court ruling striking down gay marriage bans in all 50 states. Walker has repeatedly called for a constitutional amendment allowing states to decide the issue.

“Our sons were very disappointed,” Tonette Walker said. “I was torn. I have children who are very passionate [in favor of same-sex marriage], and Scot was on his side very passionate.”

“It's hard for me because I have a cousin who I love dearly – she is like a sister to me – who is married to a woman, her partner of 18 years,” she added.

(Related: Scott Walker says presidential bid is “God's plan”; gay marriage ruling “grave mistake.”)