You can see the speckles as well as the powdery mildew.

Here is a better pic of the whole tree. I ordered it from Miller Nursery during the spring.

How can I help this tree?

At the moment I cannot see photos due to a bad video card. Many time fungicides are preventative. Try Lime Sulfur spray, it can be used to treat leaf spot and powdery mildew. You need to spray preventatives in the future. Use both sulfur and copper. Spray separately 3 weeks apart around Thanksgiving (after leaf fall), Christmas, and before bud break Feb-March. Best to make sure you read labels and that it is ok to use on tart cherries. Copper and sulfur are organic, but copper is very toxic to everything. I know it can be used on sweet cherries, probably tart too, check label!
Serenade can also be used for the mildew. Cherry trees are very difficult to grow because so many pests love them too! I have 2 sweet cherries in ground. The preventative sprays have worked, no problems. I skip the Christmas spray, but after leaf fall and before bud break are crucial. The fungi will live in buds and will come out with leaf break if not sprayed. You also probably need to spray for bugs.
Else you may find maggots in the cherries. Check with your local extension office as to what to spray. I myself do the following during growth but after petal drop not to hurt the bees.
Spray every 7 days with Bonideî Fruit Tree Spray as a preventative measure. Cease spraying 14 days before harvest. No more than 4 applications per year.

Spray every 7 to 10 days or after rain with Bonideî Citrus, Fruit & Nut Orchard Spray as a protective spray for fungal diseases. May be used up to day before harvest.
Monterey Fungal Fighter can be used instead. It is an excellent product, but read all labels!

Drew51, thank you for the advice. I contacted the company that made the sulfur/organic fungicide and expressed that the product did not work. To my surprise they decided to send me their next more expensive product on the fungicide line. It is a concentrate that will make up to four gallons of spray.

I will take your advice and use this in intervals around Thanksgiving. I also have All Season Dormant Horticulture Spray. Any suggestions on how to use this in conjunction with the fungicide spray?

I will look into Bonideî Fruit Tree Spray in the future, but would like to work with what I have for now.

Also one last question: I live in zone 6 so if I do a Christmas spray it will be down below freezing - is that safe for the tree? I can email you the pictures if you would like to see, but it seems like you have a good idea what is going on.

I don't think you can mix the sulfur and dormant spray? I think that is oil, and yeah a good product. If you use powdered copper sulfate, you can mix that with the dormant spray. You need a pump sprayer for sure. Add spray and water first, then add the copper. Mix well, keep mixing. Copper is the most effective product mentioned.
Skip the Christmas spray. That advice came to me via the west coast. I'm in zone 6 too. I skip it. I may though do 2 late winter/spring sprayings. I would highly suggest to use the copper. I use a oil sticker, but I too recently bought the dormant spray and plan to mix. Here in MI every cherry grower uses copper. Spraying one tree is not going to damage the environment any more than it already is, and it is considered organic, but very toxic for sure. Not to us, to the environment. It is extremely safe for us. I would suggest any spring pruning you do, spray right after the pruning. MSU suggests you spray before you prune, and right after to avoid any possible fungal infection.
It is very responsible to see if you have other problems before using an in season pesticide. The dormant sprays though are absolutely needed and crucial.
Use both dormant-copper, and a sulfur spray 2-3 weeks apart. I would do the sulfur first. The copper should state what you can mix it with. If you need further advice, or want to hear what orchard growers do, pose this question in the orchard forum. It's where I hang out. Those guys are awesome and know what they are doing. They have loads more experience than I do.