Dear Future President of the USA,
We are going through a very severe recession and we need your help. If you have not discovered time travel there is nothing you can do, so please re-seal this envelope and leave it for the next President.
If you have discovered time travel, then please send all of your gold back in time to (insert date here) and bury it 500 metres underground at precisely latitude (X) and longitude (Y). That date, for us, is in the future, and that is a secret location that we know hasn't been touched and therefore won't be discovered by anyone except us.
You will not lose your gold because all the gold will still be around when you become President a long time from now. All the gold we currently have will also still be around, so really you'll have twice as much gold. In fact, that means that you can send back only half your gold because if you've already done this before then technically that's our gold anyway.
However, if you insist on being paid for your gold, that's fine. We'll put a million dollars in a savings account and with compound interest it should buy a lot of your gold. So in the end what we're really asking you to do is to send our gold back to us, and you're even getting paid for it as if it was yours.
Also, if it's not too much trouble, could you also send back a Sony PlayStation 4 for my son? That's probably something you can find in a garage sale for 50 cents, but he really wants one.