HaGaon HaRav Chaim Kanievsky says Americans can carry guns to the synagogue on the Sabbath for self-defense.
Yeshiva World News reports that the question was specifically framed around having “armed guards” at synagogues, due to an increase in antisemitic incidents.
Harav Chaim spoke against posting guards but made clear that worshipers could carry firearms to the synagogue if the purpose was saving life.
The question was followed by asking if it is allowable to carry guns to synagogue even if a threat against worshipers is only potential, rather than “immediate.” Harav Chaim said it is allowable.
On October 27, 2018, an attacker killed 11 innocents at the Tree of Life synagogue in Pittsburgh, Pennsylvania. There was no armed security at the synagogue at the time of the attack.
On April 27, 2019, an attacker killed one innocent and wounded three others by opening fire on Chabad of Poway in San Diego, California.