The two oldest members of the U.S. Senate convened a four-witness hearing Tuesday to discuss concerns about marijuana legalization, but chose not to invite anyone supportive of the policy or with direct experience administering recreational pot laws in Western states.

Drug reform advocates denounced the hearing as a poorly informed waste of time, and senators most supportive of reforming federal marijuana laws did not attend.

Sens. Chuck Grassley, R-Iowa, and Dianne Feinstein, D-Calif., called the hearing of the Caucus on International Narcotics Control last month after a Government Accountability Office report said the Justice Department wasn’t documenting its monitoring of enforcement guidelines laid out by the Obama administration in 2013.

The guidelines were contained in a memo allowing for the first state-regulated recreational pot markets in Colorado and Washington, despite marijuana possession remaining a federal crime. There are eight enforcement triggers in the guidelines that could prompt federal intervention, including the distribution of marijuana to minors, negative health consequences or the smuggling of marijuana across state lines.

Opponents of marijuana legalization believe a closer look at Colorado and Washington could reveal that federal intervention is warranted. And the Justice Department, should it seek to shut down state-regulated pot markets, likely would have a better case than neighboring states, anti-pot sheriffs and anti-drug groups – all of whom have lost in court.

But supporters of marijuana legalization say the sky hasn’t fallen and were enraged that Grassley and Feinstein, each 82 years old and leaders of what's informally called the drug caucus, opted not to include anyone on their panel who would say so.

Polls generally show majority support for marijuana legalization among Americans, with support higher among young adults and lower among senior citizens.

“The outcome of the hearing has been predetermined: This is going to be a prohibitionist party, not a substantive hearing,” Michael Collins, a deputy director with the Drug Policy Alliance, said before the event. “It’s a waste of time, a waste of taxpayer dollars.” The medical marijuana advocacy group Americans for Safe Access denounced the gathering as "yet another lopsided hearing against medical cannabis."

Though no Colorado or Washington state official was invited to speak about compliance with the enforcement guidelines, Nebraska Attorney General Doug Peterson was asked to share his view of their work. Peterson, a Republican, unsuccessfully asked the Supreme Court to end state-regulated recreational marijuana sales in Colorado.

Other panelists included Sacramento-based U.S. Attorney Benjamin Wagner, who has aggressively prosecuted marijuana cases; an advisory board member for anti-legalization group Smart Approaches to Marijuana, Dr. Kathryn Wells; and the GAO official who wrote the report urging the tracking of data.

During the hearing, Wagner broke some news by announcing that the Justice Department is preparing a public website that will track statistics on marijuana.

But the pitfalls of inviting one side of the debate and not the other quickly became clear.

Feinstein was not challenged when she claimed that use of marijuana among 12- to 17-year-olds has “escalated dramatically in the states that have legalized marijuana.” It’s not clear that’s actually the case: In Colorado, use of marijuana by high school students saw a statistically nonsignificant drop from 2011 to 2013, the first year possession was legal for adults 21 and older, according to a state health department survey.

Such a dramatic escalation, if it occurred, did not warrant mention in annual reports on Colorado and Washington from the Substance Abuse and Mental Health Services Administration, which surveys 12-to-17-year-olds. Though pot use wasn’t broken out, it’s the most commonly used illegal drug, and overall illicit drug use hardly budged.

In Colorado, the age cohort’s past-month drug use ticked up only slightly from 14.4 percent in 2012-2013 to 14.6 percent in 2013-2014, and in Washington it fell from 11.5 percent to 11.4 percent. Drug dependence ticked down in both states, where retail pot stores serving adults 21 and older opened in 2014.

Nationwide, marijuana use among teens remained about the same between 2014 and 2015, according to the University of Michigan-administered Monitoring the Future Survey, which did not track state-specific data. The 2015 results of the biennial Youth Risk Behavior Surveillance System, another large government-funded survey, have not yet been released.

Following Feinstein, Grassley displayed charts on pot-related hospitalizations, the data for which he attributed to the regional law enforcement entity Rocky Mountain HIDTA, or High-Intensity Drug Trafficking Area. The accuracy of some of that task force’s reporting has been called into question, specifically its claim that Colorado-originating marijuana packages intercepted by the U.S. Postal Inspection Service have increased. Spokespeople for the USPIS deny it possesses such numbers, with one postal inspector telling U.S. News task forces "have to show they are being functional and show they are doing work to continue to receive funding."

But rather than offering a word of caution, Wagner told Grassley “that data is alarming and I’ll start off by saying the U.S. attorneys' offices are acutely aware of the data and reports that are being put out by the HIDTAs. I know my colleague in the District of Colorado is in touch constantly with the Rocky Mountain HIDTA.”

Sen. Jeff Sessions, R-Ala., one of just four senators to attend Tuesday's hearing, lamented that years of work “trying to send that message with clarity that good people don’t smoke marijuana” has been reversed. He said “the result of that, to give that away and make it socially acceptable, creates demand and results in people being addicted or impacted adversely.” Nobody offered a rebuttal that although statistics show perceptions of risk are falling nationally among youth, their use of pot is about the same.

Reform groups said the hearing was a distraction from momentum toward progress through legislation such as the CARERS Act, introduced last year by Sens. Rand Paul, R-Ky., Cory Booker, D-N.J., and Kirsten Gillibrand, D-N.Y., who are among the nation's youngest senators.

The composition of Tuesday's panel was no accident. In fact, the Drug Policy Alliance, which favors marijuana legalization, offered to help senators add a pro-reform voice to the hearing, but was rebuffed.

Jill Gerber, a spokeswoman for Grassley, says the panel did not include a pro-legalization voice or an official from Colorado or Washington because the hearing intended to focus on the Justice Department’s enforcement policy “and its commitment to keeping track of what is happening in the states, not directly about any particular state’s policy.”

“The Drug Policy Alliance wanted to have a witness on pro-legalization for recreational use and civil rights/sentencing reform,” Gerber told U.S. News by email. “These topics are afield from the hearing’s focus on DOJ enforcement and commitments.”