Mr. Rubio showed up in a standard-issue dark suit and blue tie. Mr. Paul, following Mr. Rubio to the lectern, shed his Senate uniform for a pair of jeans and cowboy boots.

Chosen to deliver the Republican response to President Obama’s State of the Union address last month, Mr. Rubio declared, “The world is a better place when America is the strongest nation on earth.” Then this month Mr. Paul electrified much of the party with a 13-hour filibuster that spotlighted the White House’s drone wars and what libertarians see as presidential overreach that threatens to extend even onto American soil.

Just days after the November election, Mr. Rubio was in Altoona, Iowa, with his name in lights, honoring Gov. Terry Branstad at his politically tinged birthday party. Not to be outdone, Mr. Paul will headline the Iowa Republican Party’s marquee Lincoln Day Dinner in Cedar Rapids on May 10, making an early venture into the state that could become a second home, should he decide to run for president.

“When you go to Iowa, people tend to take notice, so part of the reason to go is to advance the message we want as far as growing the Republican Party,” Mr. Paul said. “Going to Iowa and going to any of those states that people seem to pay a lot of attention to helps to draw attention to the message, and the message we have is, we need a more inclusive party, we need a bigger party, not a smaller party.”

As reporters swarmed Mr. Paul on Tuesday to get his thoughts on immigration and his trip to Iowa, Mr. Rubio was on CNN declaring that Justin Timberlake might be a talented performer but he was not in the league of one of his favorites, Tupac Shakur.