And for calling it a down-payment.
Remember that Exxon paid out only a fraction of its true liabilities.
With the $20 billion escrowed, BP can't tap back into it or influence the payouts, as the fund is independently-managed.
With a more-than-$4,000-per-barrel fine assessable against BP's spilled oil, along with state and local fines, fees and other legal claims (criminal, possibly, also), BP may yet look for a merger, or bankruptcy filing.
In which case, Obama's $20-billion-in-hand will look like pretty smart negotiating.