SAN JUAN, Puerto Rico (CNN) -- Sen. Marco Rubio said Friday all presidential candidates should have a strong command of foreign policy challenges before taking office, suggesting that voters should be troubled by Donald Trump's apparent lack of knowledge about Hezbollah, Hamas and other terror groups.
"If you don't know the answer to these questions, then you are not going to be able to serve as commander and chief," Rubio told CNN in an interview here.
"This should be part of the reason why you are running because you understand the threats that the world is facing, you have deep understanding and you understand what to do about it," Rubio added. "And if someone doesn't, I think it is very concerning."
Rubio, a Florida Republican and member of the Senate Foreign Relations Committee, did not criticize Trump by name. Rubio disagreed that the questions from conservative radio host Hugh Hewitt where Trump appeared to confuse Iran's elite Quds forces and the Kurds on Thursday were "gotcha" questions, as Trump suggested.
"No, I don't," Rubio said. "National Security is the most important obligation of the federal government. If you are going to be a presidential candidate, you need to take this seriously. And I think that is important."
Trump, whose candidacy has upended the Republican presidential race, said he would "find great people" and be prepared by the time he reached the White House. He dismissed questions from Hewitt as "ridiculous."
While Rubio said presidential contenders should not be expected to memorize the names of all foreign leaders or heads of terrorist groups, he believes voters should demand candidates take more than a learn-on-the-job approach to the presidency.
"It is important to have a detailed understanding of the threats we face as a country," Rubio said. "You are commander in chief on day number one and you may have to make national security decisions right away. And it takes time and dedication and a natural curiosity and interest in these issues."
As the campaign enters the next phase, Rubio said he hopes voters begin to pay closer attention to the specific policy positions of the candidates. He stopped short of targeting the Republican front-runner by name, declaring: "I'm not running against Donald Trump or Jeb Bush or Chris Christie or anybody else. I'm running for president."
Rubio made his comments during a campaign visit to Puerto Rico, a U.S. territory, which sends delegates to the Republican and Democratic nominating conventions. Tens of thousands of Puerto Ricans also live in central Florida, but pay careful attention to campaign visits to the island.
The visit is also an opportunity for Rubio to reach out to Latino voters, who are key to the Republican Party's attempts to win back the White House. He declined to wade into the escalating fight between Trump and Jeb Bush. Earlier this week, Trump suggested Bush should speak English, not Spanish, while in the United States.
"That is his opinion," Rubio said. "I am here in Puerto Rico, I am going to get asked question by Spanish media, I am going to answer in Spanish. I don't want some translator to translate what I said."
While Rubio said he speaks Spanish to his family in Miami, he added:
"But English is, in my opinion, the most important language in the United States, by far. "