Hillary Clinton is consolidating a substantial lead over Donald Trump less than a month before Election Day, picking up support from women and swing voters as the Republican navigates growing allegations of unwanted sexual contact, a new Wall Street Journal/NBC News poll finds.

Heading into the final presidential debate in Las Vegas on Wednesday, Mrs. Clinton led Mr. Trump by 11 percentage points among likely voters, 48% to 37%, a big jump from the six-point edge she held in mid-September.

The...