Treading water is certainly useful, but at some point it’s either sink or swim.

The Mets may have reached that juncture in their schedule that tells them if they are swimmers or sinkers. Three games against the Cubs at Citi Field beginning Tuesday night will have all the trappings of a postseason series, albeit with the visiting players holding a decided advantage: even if they get swept, they will still be very much alive in this NL wild-card race.

But the Mets lack such a safety net. If a repeat performance of last weekend occurs and they get swept three games to finish this homestand, the Mets’ postseason chances could be reduced to rubble by the time they arrive in Philadelphia on Friday.

The Mets trail the Cubs by two games for the NL’s second wild-card berth, with the Phillies and Brewers also in hot pursuit. And the Mets are well aware of the landscape.

“You can’t help but look,” Michael Conforto said. “There’s a group of guys watching, seeing what’s happening, but we all remind each other that if we just take care of business here we won’t have to worry about all that stuff. Everything else that is going on we can’t control, so we may get some help, we may not. You can’t worry about anybody else.”

The Mets were gangbusters in sweeping three games against the AL wild-card-leading Indians last week at Citi Field. The smackdown began Friday with a loss to the Braves in 14 innings, which preceded a shaky Zack Wheeler performance and then a beatdown by Dallas Keuchel in the series finale.

It has left the Mets at .500 on the homestand and fortunate the Cubs, Phillies and Brewers have done little to improve their own situations lately. The Cubs (69-61) just lost three straight games to Washington and hardly have the aura of the ivy-covered wallbangers who won the World Series in 2016. But that may have been evident to the Mets in June, when they split a four-game series with the Cubs at Wrigley Field.

“We played well in Chicago, there were some hiccups that stopped us from winning the whole series, but we are confident,” J.D. Davis said. “This is just a little speed bump, what’s going on right now.”

Seth Lugo’s eighth-inning implosion in the final game of that series sent the Mets spiraling: In the postgame, manager Mickey Callaway cursed out a reporter before Jason Vargas had to be separated by teammates from the scribe. The Mets followed with four straight losses in Philadelphia, with the bullpen directly responsible in three of them.

“That was a pretty tough stretch for us and we felt like we were kind of starting to build momentum in that [Cubs] series and a couple of mistakes beat us late in that final game and we couldn’t end up rallying to come back,” Conforto said. “We just have to play the type of baseball we were playing against the Indians. We didn’t bring the bats against the Braves. We were one hit away from a different outcome in all of the games, but it’s not like we got blown out in that series. We were in all of them. We played the tough and didn’t do enough to win. ”

Marcus Stroman is scheduled for Tuesday’s start, followed by Noah Syndergaard and Jacob deGrom. The Cubs have Yu Darvish, Kyle Hendricks and Jon Lester lined up for the series.

“It’s good for us as a young group to get in these situations, these big type of games,” Davis said. “A lot of energy, but it’s good for us.”