A day after Venezuela's exiled opposition leader returned to Caracas with great fanfare, U.S. Secretary of State Marco Rubio issued a veiled warning against interfering with the country's fragile democratic transition pushed by the Trump administration."You're not going to street-protest your way into a democracy," Rubio told reporters Monday without explicitly mentioning Maria Corina Machado. Why it matters: Machado's demands for elections next year — and her criticism of a massive U.S. oil deal struck with the current Caracas regime — have put administration officials on edge after her surprise return."Rubio is on a political edge," said a White House source familiar with his thinking. "Venezuela is the top foreign policy achievement of this administration, and if the progress we made gets undone and Machado is a spoiler, nobody wins."A Machado spokesperson didn't return messages seeking comment.Zoom in: Machado and U.S. officials agree that Venezuela needs to hold elections. But she has demanded they be held in 2027, while U.S. officials aren't sure. They want three things to happen first:Reform Venezuela's Supreme Court. It's stocked with loyalists of Nicolas Maduro, who was s…