Lest there be any doubt that Sen. Marco Rubio ­
(R-Fla.) is training for his presidential run (it’s a marathon, not a sprint), he teased a preview this week of a matchup against Hillary Clinton.

And like the arguments of so many whippersnappers before him, his would pit the future against the past. Or, put another way, the young vs. the old.

Late Tuesday, Rubio’s leadership PAC fundraised off an NPR interview in which the senator said of Clinton, “I just think she’s a 20th-century candidate.”

At the end of the e-mail was a P.S.: “Clinton’s ideas are from the days of the Macarena, Prodigy Internet, and the Y2K scare.”

(Ah, the ’90s. Reminds us of when Madeleine Albright taught a colleague from Botswana the dance on the floor of the United Nations. You can watch that at wapo.st/macarena.)

So, if Clinton runs, the Rubio campaign’s attack strategy will be like watching reruns of VH1’s “I Love the 90s,” reminding us of grunge fashion and Dave Matthews? Most of Clinton’s would-be challengers are in their 40s, so they should pay attention to how Rubio’s attack lands.

While Rubio doesn’t — and won’t — mention Clinton’s age outright (she’ll be 69 on Election Day 2016), the implication is clear. We caution Rubio and the other younger pols to be careful, or they could fall into the same trap Walter Mondale did when he challenged the much older President Ronald Reagan.

Reagan, asked about his age during a debate, said: “I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent’s youth and inexperience.”

Burning questions

The Defense Department is being asked to explain why solid waste was burned openly at an air base in Afghanistan when two fully operational incinerators were available.

A report released Tuesday by the Special Inspector General for Afghanistan Reconstruction is part of an ongoing investigation into why U.S.-taxpayer-funded incinerators are going unused at many bases. It comes as the family of a 46-year-old Texas man who died this month blames his death on his exposure to the toxic air emitted from burning the military bases’ waste in the open. David Thomas was a veteran of the Afghanistan and Iraq wars who died of lung cancer that spread to his brain.

The investigators looked into an air base in Afghanistan where, after receiving two incinerators in August 2012, personnel continued to burn its garbage in open pits. The Shindand air base is home to 4,000 U.S. and Afghan military and civilian personnel. The incinerators were part of a $4.4 million solid-waste-management contract for Shindand.

The watchdog recommends that the U.S. Central Command look into some unanswered questions: Why did the U.S. military continue to use the burn pits after its incinerators were fully operational? And why was Congress never notified that they weren’t being used, which is a requirement by law?

The investigators also want the United States to look into why the Afghans had never used the incinerators “we provided.” But the Central Command has said it’s not its role to make the Afghan National Security Forces use them, though it would continue to encourage it. It also said the Afghans don’t assess the health risks as serious enough to warrant the cost of fuel to run the incinerators.

Bachmann returns?

Loop fans, dry your tears. Michele Bachmann may not be leaving politics after all.

When Bachmann (R-Minn.) announced last year that she would retire at the end of this term, we wondered how we’d fill the void. She has provided much fodder over the years, especially during her 2012 presidential bid.

In March, she won the Loop Quote of the Week when she proposed that people who criticize billionaire GOP contributors should be prosecuted under racketeering laws. In May, she took a tough stand against a proposed National Women’s History Museum three years after she said she was happy, even “humbled,” to be included in its online exhibit “Profiles in Motherhood.” And who can forget her badgering for campaign donations in 2012 — “make an immediate donation,” one e-mail demanded.

But just as we were getting used to the idea of a political sphere without Bachmann, she teased Tuesday that she might just give a run for the White House another go.

“The only thing that the media has speculated on is that it’s going to be various men that are running,” she told RealClearPolitics in an interview. “They haven’t speculated, for instance, that I’m going to run. What if I decide to run? And there’s a chance I could run.”

Bachmann was among the first GOP candidates to peak (and then fall) during the 2012 primaries as voters battle-tested Mitt Romney alternatives. That experience, she said, gives her an advantage if she tries again. After all, she mused, “like with anything else, practice makes perfect.”

Just ask her state’s former governor, Harold Stassen, who legendarily ran for the GOP nomination for president nine times between 1952 and 1992.

Yes, running for the nation’s highest office is just like learning a musical instrument. It takes practice.

— With Colby Itkowitz

Twitter: @KamenInTheLoop, @ColbyItkowitz