Republican Senate nominee John Deaton used Tuesday night’s WBZ debate to cast himself as an independent-minded alternative to Democratic Sen. Ed Markey, arguing that voters should send someone to Washington who would put Massachusetts and the country ahead of party loyalty. Markey countered that Deaton’s claim to independence conflicted with his Republican affiliation and financial support for the party. Markey said Deaton had given $350,000 to the Republican Party to secure the nomination and accused him of trying to present himself as both a Republican and an independent. The candidates also clashed over U.S. military action. Both criticized former President Donald Trump’s conflict with Iran, which Deaton called illegal and foolish. Deaton then accused Markey of failing to criticize military actions by Democratic presidents, saying he would call out presidents from either party. Markey repeatedly redirected his attacks toward Trump, saying the former president had harmed Massachusetts’ economy and targeted Markey’s neighbors in Malden. Deaton landed several forceful challenges during the hourlong debate, but Markey avoided extended exchanges over them and returned to his criticism of Trump. The race is taking place in a state where Trump’s standing is weak. A RealClearPolitics average cited in the debate coverage showed Deaton trailing Markey by 23 percentage points. The same coverage reported low Trump approval among Massachusetts Democrats and independents, a political headwind for a Republican candidate seeking support outside his party. Deaton’s pitch was aimed at independents and Democrats dissatisfied with their party, but his criticism of Trump and refusal to vote for him could also complicate efforts to consolidate Republican support. The debate underscored the challenge for Deaton: making a case for himself as a bipartisan choice while running under the Republican label in a state where Trump remains unpopular.