After 3.e3, the most popular continuation is 3...Nf6 4.Bxc4 e6 5.O-O (5.d4 transposes to a Queen's Gambit Accepted [QGA; ECO D26-29]), where Black doesn't even try to keep the Pawn. Now 5...c5 6.d4 is again a QGA, where the most consistent move is 6...a6. Black can continue instead 6.b3, but will probably play d2-d4 sooner or later. • If Black tries 3...Be6, White can recapture the Pawn with 4.Na3.
Black can also recapture the c-Pawn with the Knight. After 3.Na3, Black has 3...a6 followed by 4.Nxc4 b5 5.Ne3 or 3...c5.
Not so good for White is 3.Qa4+, when the Queen will end up misplaced on c4.
