I don't think I understand the question. Are you saying that no Prime Minister before Churchill was popular?

Churchill is a bad case for "popular." He came to office as the successor to the successor to a victorious general election leader, and was easily ousted from power at an election that occurred at the same moment he triumphed over Nazi Germany. He actually won a general election only after conceding not to walk back principles of socialism and decolonialization he'd staunchly resisted his entire political life.