BOSTON — Democratic U.S. Sen. Elizabeth Warren and her Republican challenger, state Rep. Geoff Diehl, are set to face off in their first debate of the campaign. The two will go head to head tonight at 8 in the televised debate on WSBK-TV. The debate will also be streamed live on www.CBSBoston.com. Warren, a potential candidate in the 2020 presidential campaign, is running for her second six-year term representing Massachusetts in the Senate. Diehl, who co-chaired President Donald Trump's 2016 Massachusetts presidential campaign, is hoping to unseat Warren who has been a frequent critic of Trump. Warren on Monday released...