The word ‘allowed’ is doing some truly Olympic-level heavy lifting there. The United States, which has two Coast Guard cutters in the region that could have intercepted the tanker, chose not to.
In other words: they allowed it.
but because it was in no position to start a fight with Russia while its fleet is already stretched thin bombing Iran.
Wut. Ukraine has been embarrassing their 3 day operation for years now. The US would steamroll them into a nuclear war in 3 days. That is why they back down: the inevitability of nukes. It's the only thing russia has going for it nowadays.

In reality, the reasons for US behaviour are far more nefarious and/or embarrassing having to do with either Trump's senility or jealousy of putin. The author of this shitstack article needs to take their head out of their ass.