It might help if you had some idea with what Tucker is mixed with…......if you look around the forums here you will not find it uncommon for basenjis to become less tolerant (ruling out any medical issues) of other dogs at about 2 years or so. My dog is about three now; he also underwent a change in personality, and became less willing to entertain 'rude dogs' or puppies over time. ................but there is a not-so-fine line between growling and aggression.
If your dog is physically harming other dogs, that needs to be taken care of immediately. If your dog is fighting with other dogs, or growling, but not leaving marks or biting.......you have room to work on whatever is going on. A dog needs to be able to defend himself through body language provided they don't escalate to violence, or provoke other dogs. A reactive rover class might be worth checking out.
Leash aggression is very common in dogs of all breeds; is he ok when off leash with other dogs? If that's the case then it might help to switch to a harness,. Anything pulling on my dog's neck will aggravate leash aggression.
Prevention is your best friend; it would be best to avoid all dog parks, or other dogs, as much as possible. An eye contact command; getting his attention off other dogs and on to you for when other dogs can't be avoided.
I think aggressive gets thrown around in our society a lot....a truly aggressive dog is not easy to deal with at all. The owners of these types of dogs have a responsibility to keep their dogs out of the public, away from other dos, as much as possible. These would be dogs who have mauled people or killed other dogs. These dogs are very hard to rehabilitate and are either 1.) put down or 2.) need to be locked up for the rest of their lives.
My guess - based on little information - is that Tucker is merely communicating as dogs do. It's my personal (and unfounded) opinion that dogs should absolutely be allowed to defend themselves without reprimand; but with the owner making sure the situation is deescalated, and provided that he's not leaving marks. If he is not actually hurting other dogs - but nipping at them, or snarling as a warning......he's trying to get a message across. In that case it might help to work on any fear issues he might have.
Aggression is an all encompassing term. As pointed out above, there is quite a range! It is not unusual for Basenjis to be dog aggressive. Mine is, and I just avoid other dogs because I know his intentions are not good. Some are same sex aggressive and fine with members of the opposite sex, and some may just be making a statement when they are leashed. If you describe what you are seeing more specifically I am sure lots of people will have common experiences and possible training fixes to share.
I would love to see some pictures of Tucker, and welcome to the forum!