WASHINGTON — Since taking office in 2010, U.S. Sen. Marco Rubio has cultivated an image as a serious foreign policy thinker who has never missed a chance to weigh in on current affairs — or to criticize President Barack Obama.

But in the past few days as Obama readied military strikes against Syria, the Florida Republican was notably silent — a reticence reflecting both the lack of easy answers and how Rubio's hawkish outlook is being challenged by a rising libertarian strain in the GOP.

Rubio finally weighed in Wednesday evening, after many other politicians had. He said Obama should have acted much sooner to identify allies in Syria and "help train and equip them so that they could not only topple (President Bashar) Asaad, but also be the best organized, trained and armed group on the ground in a post-Assad Syria."

But even as he criticized Obama, Rubio too reflected the unclear path ahead. He did not address the kind of strikes being contemplated and offered divergent thoughts: That the president come up with a plan to use "all of the tools at our disposable that stands a reasonable chance" or "simply focus our resources on helping our allies in the region protect themselves from the threat they and we will increasingly face from an unstable Syria."

The debate over Syria and U.S. engagement abroad comes amid a GOP tug-of-war between neoconservatives such as Rubio and a rising libertarian-minded wing that wants to pull back. The American public is war weary, too.

"The war in Syria has no clear national security connection to the United States and victory by either side will not necessarily bring in to power people friendly to the United States," Sen. Rand Paul, R-Ky., said in a statement Wednesday.

Paul, a possible 2016 presidential opponent of Rubio, said the U.S. should investigate the use of chemical weapons and have "an open debate in Congress over whether the situation warrants U.S. involvement."

(Rubio in his statement, which came hours after Paul, also said Obama must "clearly lay out to Congress and the American people why this is in our national interest.")

While Rubio remained silent, Florida Democratic Sen. Bill Nelson was unequivocal.

"There should be moral outrage over the use of chemical weapons on innocent civilians in Syria," Nelson said Tuesday. "At this point I believe it appropriate to take military action with NATO and our regional allies. Inaction would only lead to greater suffering and instability in the region and would further embolden Assad."