I disagree...nobody can just call in this situation since you are just begging to get reraised. Most likely this is an attempted steal and he can literally have any two cards. If you want to go a step further to figre worst case you might also assume that no other player had an ace since they all folded and they also might try to steal with Ax and would likely come in with AT+....so remove 14 cards from the desk and assume 3 aces left and a better kicker... about an 8% chance. Throw in the chance of a pair of 4's or better and you are still only around 12%...far less than the 20% you already have in the pot which makes up for any chance that you might not be favored.