A federal judge in Manhattan has dismissed a lawsuit filed by the Democratic National Committee against Russia, the Trump campaign, WikiLeaks and others, ruling the committee’s allegations of a wide-ranging conspiracy to interfere in the 2016 election were “moot or without merit.”

The lawsuit, filed in April 2018, alleged the defendants conspired to hack into the DNC’s computer network and strategically leak stolen information to undermine Hillary Clinton’s presidential campaign and improve Donald Trump’s odds of winning the...