Congressional hearings designed to help unravel details behind the September consulate attack in Benghazi, Libya, morphed into a battleground Thursday as Democrats and Republicans sought to position themselves and their parties for the months and even years ahead—including in 2016, the next presidential election year.

Sen. John Kerry (D., Mass.), chairman of the Senate Foreign Relations Committee, used his lectern Thursday to articulate views on American foreign policy that went well beyond the Benghazi assault, and called for a well-funded and diplomatically aggressive State Department to emerge in the coming year. President Barack Obama is expected to nominate Mr. Kerry as the next U.S. secretary of State to succeed Hillary Clinton.

Republicans lawmakers, meanwhile, took the opportunity during Senate and House hearings Thursday to hone criticism of Mrs. Clinton, a possible future presidential candidate, for her role in addressing growing terrorist threats in Libya, leading to the September assault and the deaths of U.S. ambassador, Christopher Stevens and three other Americans.