Voters in Mexico Cement the Governing Party’s Dominance

The margin of Claudia Sheinbaum’s election as Mexico’s president was the biggest in decades, and even as the votes were still being counted on Monday, it became clear that Mexico’s leftist governing party and its allies could be in a position to reshape the country’s political landscape.

They appear on the verge of claiming large enough majorities in Congress to enact proposals to change the Constitution that have alarmed the opposition, including advancing contentious legislation that could potentially dismantle crucial checks on presidential power.

Ms. Sheinbaum, the first woman and first Jewish person to be elected president, beat her opponent on Sunday by a stunning 30 percentage points or more, early returns show. She and her Morena party had been expected to win, but their resounding victory outperformed pre-election polls.

“We’re taking the whole shebang in these elections,” Mario Delgado, the head of the Morena party, said in a speech Sunday.

The election served as a referendum on the nearly six-year term of Andrés Manuel López Obrador, the current president, reflecting that a solid majority of the electorate has endorsed his stewardship of the country.

Preliminary results show Morena taking seven of the nine governorships up for grabs — including the most prominent, Mexico City’s — and winning supermajorities in at least 22 of the 32 state legislatures.