By Steve Holland and Andy Sullivan PALM BEACH, Fla. (Reuters) -Donald Trump, who has mounted relentless attacks on the integrity of U.S. voting since his 2020 election defeat, on Tuesday launched a bid to regain the presidency in 2024, aiming to pre-empt potential Republican rivals. Seeking a potential rematch with Democratic President Joe Biden, Trump made his announcement at his Mar-a-Lago estate in Florida a week after midterm elections in which Republicans failed to win as many seats in Congress as they had hoped. In a speech lasting little more than an hour, Trump spoke to hundreds of sup…