Many of the protesters wore shirts reading "Jews say ceasefire" and "not in our name."
The briefing was organized by the JFNA together with SCN (Secure Community Network), ADL, and the OU (Orthodox Union), with the support of six other major Jewish organizations.
People inside the US Capitol during summer recess were urged to take shelter immediately.
Former US vice president and Republican presidential candidate Mike Pence said he felt President Donald Trump's words and actions leading up to the Capitol attacks were reckless but not criminal.
A new report holds government agencies responsible for downplaying the threat of the Jan. 6 attack on the US Capitol, even as it was happening.
"This is not a Republican or Democrat issue," a coordinator of Concerned Citizens of NY-03 said.
McCarthy faced fierce opposition from within the Republican caucus, as 19 members defected in the first round – which took place on Tuesday.
"The current threat climate, particularly against elected officials, will require continued and heightened vigilance," USCP Police Chief Tom Manger said in a statement.
For US Jewish organizations, the new Congress will mean seeking consensus between Republicans and Democrats to promote bills on issues important for the community.