(a) TOSFOS (DH Lo Nechleku) and RABEINU CHANANEL rule that neither needs
Hatafas Dam Bris. They rule in accordance with Rav, who argues with Shmuel
and says that the Halachah is like the Tana Kama's version of Beis Hillel's
opinion. Beis Hillel, according to the Tana Kama, says that a baby born
circumcised does not need Hatafas Dam Bris. Consequently, a convert
certainly does not need Hatafas Dam Bris, because the requirement of
Hatafah for a baby is more strict than that for a convert. (This hierarchy
is evident from the Gemara, where we find that even according to the
opinion that maintains that a baby born circumcised *needs* Hatafas Dam
Bris, a convert does *not need* Hatafah).
(b) The BEHAG says that a baby born circumcised does not need Hatafas Dam
Bris, like Tosfos says, because we follow the ruling of Rav. However, the
Behag rules that a convert who was already circumcised *does* require
Hatafah (basing his ruling on a Gemara in Yevamos 46b). This seems to
contradict the logic of our Gemara, which implies that a convert needs
Hatafah to a *lesser* degree than a child born circumcised.
Tosfos, in the name of Rabeinu Shimshon, explains that indeed logic would
require that Hatafas Dam Bris should be necessary for both a circumcised
gentile and a baby born circumcised. However, the Tana Kama derives from
the word "Orlaso" in the verse that not only is Hatafas Dam Bris *not*
performed on Shabbos (as stated earlier on this Amud), but it is not
required of a born-circumcised baby at all. However, that verse was stated
only with regard to a baby, and not with regard to a convert. Therefore,
with regard to a convert the logic that Hatafah is required remains, and
thus a convert needs Hatafas Dam Bris.
To elaborate on the logic behind this statement we can suggest that the
convert may need Hatafah because he was born with an Orlah. The Torah
considers someone who was born with an Orlah to be someone to whom Milah
can be performed. Therefore, even if he decides to become Jewish after he
cut off the Orlah he is obligated to do some action, just like the person
who still has an Orlah. This obligation is fulfilled by Hatafas Dam Bris
(ROSH).
Alternatively, perhaps a convert needs Hatafah because he must do some
*action* in order to become part of the Jewish people. He must have a Milah
not only to fulfill the Mitzvah of Milah, but also to make him into a Jew.
Even if he was already circumcised when he was a gentile, some action must
be done in order to make him part of the Jewish people. The baby, however,
is Jewish by virtue of being born to a Jewish mother, and he needs no
action to make him part of the Jewish people.
(c) The RIF and RAMBAM (Hilchos Milah 1:7) rule that *both* a gentile who
was circumcised and a baby born circumcised need Hatafas Dam Bris. The
KESEF MISHNAH explains that this ruling is based on the opinion of Rebbi
Eliezer ha'Kafar who says that Beis Hillel maintains that both need Hatafas
Dam Bris.
However, the Rambam (Hilchos Milah 3:6) rules that no blessing is recited
when Hatafah is performed to the convert. If the Rambam rules like Rebbi
Eliezer ha'Kafar, why should one not recite a blessing?
The RAN (on the Rif) explains that the Rambam is not ruling definitely like
Rebbi Eliezer ha'Kafar. Rather, the Rambam is in doubt whom the Halachah
follows, and therefore he rules that a convert needs Hatafah but without a
blessing.