Trump said he would donate $1 million to Elizabeth Warren’s favorite charity if she was Cherokee. Since she has evidence for it now, can she collect? What court(s) would/could she sue in if possible/necessary?
Possibly, but not likely, but as always facts and circumstances matter, though Trump was not very concise in what he said. First let's start off from the the transcript of what Trump said. from Politifact:
"I will give you (Warren) a million dollars to your favorite charity, paid for by Trump, if you take the test and it shows you're an Indian."
Looking at this as a contract, to have a contract you need five elements: offer, acceptance, consideration/quid por quo, capacity, and legality. It seems that all are pretty straight forward as being met except valid offer and consideration.
For the offer, you could argue Trump said it as a joke, but given that he said it to the whole world and is wealthy enough to back it up where as an average Joe would not have the cash. This comes down to what a reasonable person would have thought. Did Trump's offer seem legitimate, did he rescind before acceptance, did he repeat the offer? All of the fact and circumstances matter as to whether the offer was valid. There is also the issue of what did the contract layout as performance?
The vagueness of the contract may be an issue and make the deal illusory. For example, Trump said "a million dollars to your favorite charity" which is different than saying a million dollars to a charity of your choice. Is this Warren's favorite charity when the deal was made, or when the result were tendered, or when paid? Also there is no timeline. When must Trump make the donation? within one week, one year, one century? There is no deadline for Trump to make a donation. Also of note is the contract is for proof Warren is "Indian" (Native American), not specifically Cherokee.
For consideration you could arguee that Trump gained proof that Warren was Native American, but the issue is what did Warren gain? You could argue nothing since Trump made the promise for a donation to charity, but you could also argue that Warren gained the joy of seeing a charity get $1,000,000, Trump lose $1,000,000 and the charity was a third party beneficiary which is allowed and is valid consideration.
Even if a valid contract existed between the two, there is also the issue of what is considered performance? What does if you take the test and it shows you're an Indian. mean? May Warren be 1% native american or must she be 100% native american, the details are very vague. Since trump created the agreement, any reasonable interpretation by Warren would be permissable under the doctrine of contra-proferendum but then what is reasonable? Again facts and circumstances matter.
The available evidence indicates that POTUS made an offer related to showing that Warren "is an Indian". The "offer" does not specify which tribe, nor does it specify what it would mean to show that one "is an Indian". The federal government solves this problem by not deciding, leaving it to the individual tribe, and tribes differ in their rules: the federal government refers the question to being an enrolled member of a tribe. I think that the minimum "blood quantum" accepted by any tribe in the US is 1/16th (that is the rule for the Cherokee tribe). A reasonable interpretation, though not the only one imaginable, is that the offer meant "is legally eligible for enrollment in some Native American tribe". To support a civil claim, plaintiff would have to provide reasonable evidence that there is an ambiguity in the contract. The term in question is vague, not ambiguous – contra proferentem does not address situational vagueness.
There is no contract or any other cause of action here: there is not even an offer open to acceptance. See What is a contract and what is required for them to be valid?
Mr Trump did not intended to create legal relations - it was merely a piece of rhetoric.
Further, there is no consideration on Ms Warren’s part - “Being Cherokee” is not something that can be provided in response to the offer. Providing evidence that she is may be something that could be consideration.