Sen. Marco Rubio (R-Fla.), in his quest to reclaim stature among conservatives, visited London and delivered a foreign policy speech on Tuesday. It was an improvement in both style and substance from the phone-it-in effort he turned in a couple of weeks ago at the American Enterprise Institute.

For one thing, there was some detail in his London remarks: “In particular, the United States needs to continue to work closely with the E.U. to bring Ukraine into the Western fold. We should all be concerned about the Ukrainian government’s recent decision to bow to Russian pressure and not sign an association agreement or free trade pact with the E.U. Our thoughts are with the hundreds of thousands of Ukrainians who have taken to the streets to express concern about the future of their country.” And he issued a thoughtful call for NATO to coordinate better on its joint operations. (“We need to explore ways that NATO can prepare for its future missions. For instance, despite the sacrifices borne by many allies in Afghanistan, our militaries gained valuable experience in coalition warfare. We should determine how these capabilities can continue to be relevant in the future. We also must be frank about where we can improve our efforts. Most can agree that the operation in Libya, for example, shouldn’t have turned into such a difficult effort for the alliance.”)

But I think the utility of these sorts of speeches going through a laundry list of items is diminishing. It is not enough to spot the problems; the devil is now in the details. He observed:

Our cooperation is especially important in a Middle East that’s currently going through a fundamental transformation. It presents us with great opportunities, but also with the potential for great peril. Europe and the United States should work more closely together on tasks such as shepherding Egypt’s transition to democracy or helping Tunisia and Libya provide benefits of their new-found freedom to their citizens.

We must find ways to alleviate the human suffering of the Syrian people and work to build up elements of the moderate opposition. It should be a priority to ensure that the ongoing civil war does not create further regional instability or provide a new safe haven for al-Qaeda affiliates that would one day turn their attention toward us.

Well, that is all well and good, but what specifically does he have in mind — and wasn’t a more forceful response to Bashar al-Assad, a response he opposed, part of the formula for alleviating the suffering, that is, by hastening the end of the war?

Better, I think, for Rubio and others to focus on some of the big issues. He only would say about the most pressing national security issue of our time, “I am personally skeptical of the interim agreement that the P5+1 have concluded with Iran. I am convinced that Iran’s ultimate goal for these negotiations has been to achieve relief from the pressure of international sanctions, while retaining the option of developing a nuclear weapon. This model has been used by others in the past, such as North Korea, to successfully exploit talks to create the time and space to go nuclear.”) Maybe he felt constrained about delivering a rebuke to the administration while overseas, but he could have delivered something more meaningful than that.

Rubio might do himself, the party and the country a favor by focusing on the Iran issue and delivering forceful and unrestrained remarks. As I noted, Secretary of State John Kerry will sooner or later get up to the Hill to testify. A face-to-face encounter with the administration’s defender of the Iran pact would be illuminating. More than a set piece covering many topics, this would, I suspect, show Rubio has some gravitas. It is about time to challenge the president and secretary in a public and dramatic way.