WASHINGTON — Several prominent veteran Democrats, alarmed by the party’s drift from its longstanding alignment with Israel, are starting a new political group that will try to counter the rising skepticism on the left toward the Jewish state by supporting lawmakers and candidates in 2020 who stand unwaveringly with the country.

With polls showing that liberals and younger voters are increasingly less sympathetic to Israel, and a handful of vocal supporters of Palestinian rights arriving in Congress, the new group — the Democratic Majority for Israel — is planning to wage a campaign to remind elected officials about what they call the party’s shared values and interests with one of America’s strongest allies.

“Most Democrats are strongly pro-Israel and we want to keep it that way,” said Mark Mellman, the group’s president and a longtime Democratic pollster. “There are a few discordant voices, but we want to make sure that what’s a very small problem doesn’t metastasize into a bigger problem.”

The group, whose board includes former Michigan Gov. Jennifer Granholm and a former Clinton administration housing secretary, Henry Cisneros, will create a political action committee later this year and may engage in Democratic primaries, Mr. Mellman said. They also are planning an “early states project” with the goal of organizing pro-Israel Democrats in the first nominating states to lobby the party’s presidential hopefuls.