LAS VEGAS - Donald Trump will once again be standing at center stage when nine Republican presidential candidates debate tonight in Las Vegas.

The debate will be the first for Republicans since the attacks in Paris and San Bernardino, California, that increased concerns about terrorism in the United States. Trump's response to the terror attacks was to call for a total ban on Muslims entering the U.S. The proposal was roundly criticized by his rivals but appears to be resonating with some of his supporters.

Tonight's debate comes as Sen. Ted Cruz is trying to pitch himself as a more electable alternative to Trump. The two have maintained a friendly relationship for months, but signs of a split have emerged in recent days -- with Trump calling Cruz "a little bit of a maniac."

There's also been some sparring recently between Cruz and Florida Sen. Marco Rubio, particularly over the issue of national security.