She travels the country in white, rosaries swinging from her neck. Women cry in her arms, men beg her for salvation. Stripped of her bodyguard last week by the government, she traversed the streets unprotected.

As she climbed onto the windshield of her battered car — her makeshift stage — supporters jostled to touch her. One passed her a hand-drawn portrait. Inside the frameless image, María Corina Machado was shielded by the Venezuelan flag and the arms of Jesus Christ.

“María!” yelled one supporter, “help us!”

Ms. Machado, 56, the newest leader of Venezuela’s opposition, has struck fear into the hearts of the country’s ruling party. In a matter of months, she has emerged from the political sidelines to build a powerful social movement capable of bringing thousands of people to the streets — and perhaps millions to the ballot box.

She is not the one running for president, but she is the driving force behind the main opposition candidate, a little-known diplomat named Edmundo González.

The mobilization Ms. Machado has catalyzed follows years of political apathy in Venezuela, where the government of President Nicolás Maduro has crushed protests and arrested dissidents, helping to spur an enormous exodus from the country.