The term ‘it’s off to the races’ has been used quite a bit throughout politics … here’s just a few examples.
“There’s no difference between me and the president on taxes. No more nit-picking. Zip-ad-dee-doo-dah. Now it’s off to the races! … George Bush
… the politicians were OFF TO THE RACES, adding promise after promise of unearned benefits to those who retired by mortgaging the incomes of workers not yet born.
To me "It's off to the races" is about fraud, trump's tweet is about exposing them.