Eight Republican presidential candidates, including the dominant front-runner, former president Donald J. Trump, are set to address a gathering of Jewish Republicans in Las Vegas on Saturday, in what amounts to a test of foreign policy bona fides — and a bid for donor support — amid a rapidly escalating conflict in the Middle East.

The annual gathering of the Republican Jewish Coalition has become perhaps the highest-profile gathering of the Republican primary season, taking on greater urgency after Hamas’s attack on Israel three weeks ago.

It is also a galvanizing moment for Republican officials: In a last-minute pivot, the event’s schedule changed to accommodate the first national appearance by the newly elected House speaker, Mike Johnson, who will address the group on Saturday night.

Support for Israel unifies a broad coalition of Republican voters and officials, including foreign policy hawks, business leaders and evangelical Christians.