On Monday afternoon, Washington Nationals Manager Davey Johnson was asked for his reaction to the suspensions Major League Baseball had levied against 13 players for violating the sport’s drug policy. Johnson scarcely blinked, lauding the office of Commissioner Bud Selig and then adding, “I’m glad it’s over with.”

But Selig’s investigation into a South Florida anti-aging clinic clearly shows that baseball’s battle with performance-enhancing drugs isn’t “over with.” Indeed, experts in sports doping believe that the problems in baseball — and cycling, track and field and other sports — remain widespread and that policing sports is proving to be nearly impossible.

“This is a problem we’re going to have no matter how tough the penalties and the sanctions are,” said Steven Ungerleider, an author and psychologist who has done extensive research on doping in sports. “This is something we’re going to have to talk about for years and years and years to come.”

Start with this week’s suspensions: Each was levied without a positive drug test. So there comes one question: Even as MLB ramped up its testing policies in the wake of the Mitchell report in 2007 — it now tests blood in addition to urine and tests both in and out of season — what good is increased testing if established users don’t test positive?

“It’s a terrible predicament,” said John Hoberman, a professor at the University of Texas who has written on and taught about performance-enhancing drugs. “I think we may be at a real turning point here because what we have is simultaneous crises in a variety of major sports. You’ve got desperation on the part of the Major League Baseball commissioner’s office in terms of trying to get a handle on this. . . .

“The point of the testing is to keep the sports-entertainment industry functioning, to maintain its loyal public and to stay in business. This is a tremendous obstacle for them because the sports-entertainment industry that is trying to put an end to endless doping scandals is the same industry that is providing the incentives that lead to doping in the first place.”

Still, many experts consider testing the backbone of any doping-prevention program. “Take away testing, and it’s back to WWE, or it’s baseball in the late ’90s,” said Travis Tygart, the CEO of the U.S. Anti-Doping Agency, the organization that oversees testing in the U.S. Olympic community. And Tygart points out that the first three players to serve suspensions for involvement with Biogenesis — pitcher Bartolo Colon, outfielder Melky Cabrera and catcher Yasmani Grandal — all tested positive.

“Some of these [players] are at the top of the game, who have the resources to go to the places that give them the best guarantee that they’re not going to test positive and they’re still able to use performance-enhancing drugs with great benefit,” Tygart said. “And yet they were caught. . . . The risk of getting caught is significant.”

Monday’s suspensions, though, show some players believe it’s a risk worth taking. Alex Rodriguez — the only player tied to Biogenesis who is appealing and thus playing — is due $28 million this year, for instance. Nelson Cruz, the Texas outfielder who accepted his 50-game suspension Monday, is a free agent at season’s end, when he almost certainly will receive a contract based on the fact he has hit at least 22 home runs in each of his five seasons as a regular, not on the fact he missed 50 games in a pennant race. Finances, clearly, are an incentive for performance, regardless of the route to get there.

Would stiffer penalties — more than the current 50 games for the first offense, 100 for the second and a lifetime ban thereafter — work? Michael Weiner, the head of baseball’s players’ union, said the executive board considered that possibility last offseason and likely will do so again this winter.

“There were some players then who were clearly in favor of enhanced penalties,” Weiner said Monday. “There were some players who were clearly not. That remains so. . . . It’s going to be an interesting discussion.”

The impact of stiffer penalties, though, is dubious. “If sanctions worked, we wouldn’t be having this conversation,” Hoberman said.

The Post Sports Live crew offers advice on how to talk to your kids about Major League Baseball's Biogenesis suspensions and fallen sports heroes. (Adam Wise//)

In addition, baseball’s two major investigations into its drug problem — the queries that resulted in the Mitchell report and the seven-month process of looking into Biogenesis — hinged largely on single sources. Many of the 89 players cited in the Mitchell report had ties to a former clubhouse attendant with the New York Mets named Kirk Radomski. Without Radomski’s testimony, the Mitchell report would have been significantly weaker and baseball’s problem would not have been as publicly documented.

Similarly, the Biogenesis scandal grew because a newspaper, Miami New Times, in January exposed the company’s records, which revealed the names of several major leaguers. Officials from MLB subsequently interviewed the firm’s owner, Anthony Bosch, extensively, and Bosch’s cooperation almost single-handedly brought down the 14 players suspended over the past two weeks — the 13 on Monday, along with former National League MVP Ryan Braun, who was banned for 65 games July 22.

The singular power of those two sources — Radomski and Bosch — leads to several questions. What if investigators hadn’t found them? What if Miami New Times never committed itself to reporting on Biogenesis? And could that one small firm, tucked away in a Coral Gables strip mall, really be the only one in the nation supplying major leaguers with drugs?

“No doubt there are many, many other places,” Ungerleider said. He pointed to the investigation into the Bay Area Laboratory Co-operative (BALCO), the California firm that supplied athletes across a wide variety of sports with steroids and other drugs from the late 1980s into the 2000s. Victor Conte, the lab’s founder, said in court testimony that authorities needed to understand there were other BALCOs.

“He said, ‘Look around, you guys,’ ” Ungerleider said. “‘There’s labs all over the place.’”

Baseball players, Ungerleider said, use such facilities for two purposes: to “pre-sample” their urine or blood so when testers arrive at their doors, “they already know they’re clean.” The second is as nefarious and gets to the heart of the problem baseball — or any sport, for that matter — has in truly getting clean: Athletes are looking for masking agents that will make their samples test clean even when they’ve used performance enhancers.

“There’s a number of ‘Baby Biogeneses’ running around the universe,” Ungerleider said.

Since rampant steroid use defined an entire decade or more of baseball, Selig has taken a personal interest in giving the impression that the sport is doing everything in its power to rid itself of drugs. In a statement Monday, he said: “As an institution, we have made unprecedented strides together.”

Yet what those strides lead to, in the evaluation of experts, is far from decreased use. Indeed, as the Biogenesis suspensions begin and Rodriguez awaits his appeal process, baseball’s drug issues are far from over.

“It’s a ballooning problem,” Hoberman said.

Adam Kilgore contributed to this report.