“I think we’re open to small moves; I’m not sure we’re open to big moves,” said Mark Mellman, a Democratic pollster. “Partisanship has made our system so sclerotic that it isn’t very responsive to real changes in the real world.” Amid the mounting drama of the early summer, a moment of truth appears imminent. It is one that will reveal whether the American electorate is still capable of large-scale shifts in opinion, or whether the country is essentially locked into a schism for the foreseeable future, with roughly 53 percent of Americans on one side and 47 percent on the other... Russ Schriefer, a Republican strategist, offered an even blunter assessment of the chances for real movement in the electorate. He said that the receding of the pandemic had helped voters feel better about the direction the country is moving in — “the Covid reopening certainly helps with the right-track numbers” — but that he saw no evidence that it was changing the way they thought about their preferences between the parties. “I don’t think anything has particularly changed,” Mr. Schriefer said. “If anything, since November people have retreated further and further back into their own corners.”