Rubio gets boost from Republican endorsements, Cruz missteps

By Doina Chiacu and Alana Wise WASHINGTON (Reuters) - Republican presidential candidate Marco Rubio received boosts Monday in his drive to become the mainstream Republican alternative to front-runner Donald Trump, with a string of high-profile endorsements and missteps by rival Ted Cruz's campaign. Rubio, who eked out a second-place finish in South Carolina's primary by fewer than 1,000 votes over Cruz on Saturday, racked up endorsements from prominent Republicans including U.S. Senator Orrin Ha