Secretary of State John Kerry testifies at a Senate Foreign Relations Committee hearing on July 23 to review the Iran nuclear agreement. (Andrew Harnik/AP)

It could be sometime next year before the Iran nuclear agreement takes effect if Congress does not block it before the lawmakers’ 60-day study period ends Sept. 17.

Energy Secretary Ernest Moniz predicted that it “will be in 2016” before the International Atomic Energy Agency (IAEA) certifies that Iran has taken all the steps required and sanctions start to be lifted.

The delay will not only allow plenty of time to verify that Iran is taking preliminary steps called for in the agreement, but also for Congress and the public to weigh the facts underlying critics’ chief arguments against the pact.

In coming weeks, I plan to take up some of the most controversial items, starting with the possible military dimensions (PMD) — the IAEA finally getting answers to questions about Iran’s past research on nuclear weapon production.

Extensive intelligence going back more than a decade has been passed to the IAEA, much of it from the United States, that shows Iran pursuing warhead sizes, explosion triggers and various other elements that would lead to a nuclear weapon — as well as information about Tehran enriching uranium and seeking plutonium.

For years, and as recently as August 2014, Iran has told the IAEA that “most of the issues” raised in the PMD context were “mere allegations and do not merit consideration.”

Some critics have asserted, as Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) did at his panel’s hearing on Thursday, that when it comes to Iran satisfying the PMD issue, the signed Joint Comprehensive Plan of Action (JCPOA) between the United States, its allies and Iran “has no bearing whatsoever on whether the sanctions are removed or not.”

Other critics have questioned how the investigation of Iran’s alleged previous nuclear weapons activities is to be carried out under a confidential arrangement between the IAEA and Tehran that makes the Iranians active participants in, for example, collecting soil samples at their own suspected sites.

As Sen. James E. Risch (R-Idaho) put it at Thursday’s hearing: “We’re going to trust Iran to do this? This is absolutely ludicrous.”

Let’s address those two critical issues separately.

Although there is no direct mention of PMD in the JCPOA, it does deal with it indirectly. On Adoption Day, which is projected to be Oct. 15, the IAEA, according to the agreement, must verify that Iran has completed activities set out in a July 14 agreement between the IAEA and Tehran on settling all PMD matters.

Under that agreement, Iran must by Aug. 15 provide documents and explanations for outstanding PMD issues, and before Oct. 15 must answer any further IAEA questions and settle any outstanding “ambiguities.”

In addition, IAEA and Iran will have agreed on how to deal with access to Parchin, a military base where Iran supposedly carried out experiments related to nuclear weapons.

On Dec. 15, the IAEA is to release its final assessment on the resolution of all outstanding PMD questions.

As Secretary of State John F. Kerry put it before Corker’s committee Thursday, “PMD has to be resolved — before they get one ounce of sanctions relief.”

PMD is a serious issue, as an IAEA 2011 summary of its investigative findings up to that time showed. The agency studied thousands of pages of documents provided by U.S. intelligence, many of them from an Iranian laptop computer obtained in 2004. Information also came from 10 other countries, and on several occasions IAEA investigators interviewed former participants in the Iranian program.

For example, in 2007 IAEA interviewed “a member of the clandestine nuclear supply network” who said “that Iran had been provided with nuclear explosive design information,” according to the 2011 IAEA summary.

Information also was gathered about Iran studying how to carry out underground nuclear testing associated with something called Project 111. In that effort, Iran studied a firing system that “would enable the payload to explode both in the air above a target, or upon impact of the re-entry vehicle,” according to the IAEA summary — characteristics useful only for a nuclear weapon.

When Iran was shown this information “it dismissed [it] as being ‘an animation game,’ ” according to the IAEA.

I detail some of what the IAEA has found to show how far along Iran was before 2003, when it supposedly cut off work on the nuclear weapon itself. That bolsters the U.S. intelligence community’s 2012 assessment that Iran has “the scientific, technical, and industrial capacity to eventually produce nuclear weapons, making the central issue its political will to do so.”

Kerry put the matter more bluntly when asked Friday about Iran wanting to get the prerequisites to produce nuclear weapons. “They already have that, I mean, the horse is out of the barn on that one,” he said.

The IAEA’s past investigative work should somewhat address lawmakers’ worries about how it will handle its confidential work with Iran on the PMD issue. That confidentiality, according to the State Department, is based on a principle followed “throughout the IAEA’s existence to protect both proprietary and proliferation sensitive information.”

The PMD inquiry is not to catch Iran lying about its past activities. The information is needed to have a baseline for what Iran’s program had achieved.

David Albright, president of the Institute for Science and International Security who worked in the 1990s with IAEA inspectors, explained it this way: The IAEA wants to know how far Iran got, “where it did this work” and “was this weapons capability just put on the shelf, waiting to be quickly restarted?” With that information, the IAEA can “design a verification regime and to determine if Iran’s nuclear program is peaceful today,” he said.