Mr. Rubio, a Florida senator, defended traditional marriage. “I remind people that the institution of marriage as one man and one woman existed long before our laws existed,” he said. “Thousands of years of human history teach us a simple truth: The ideal way to raise children is when a mother and father married to each other, living in the same house, raise children together.”

At a house party nearby earlier in the day, Mr. Rubio, making his first visit here as a declared candidate, indicated he would compete aggressively in Iowa. “We want to win the caucuses in this state,” he said.

On the same night that leaders of the national press corps were dining in Washington with sundry entertainment celebrities, Mr. Jindal offered a message for “Hollywood and the media elite.”

“The United States of America did not create religious liberty; religious liberty created the United States of America,” a line that earned a standing ovation.