WASHINGTON, Jan. 11 -- The day after abruptly ending talks with Democrats, US President Donald Trump said he will "probably... may be definitely" declare a national emergency to fund his US-Mexico border wall if the impasse continued, with the ongoing government shutdown likely to become the longest in US history.

"Have the option" to do that, Trump told reporters before leaving for a border visit to McAllen, Texas on Thursday. "If this doesn't work out," he said, referring to negotiations with the Democrats, "I'll probably will do it, maybe definitely."

He could announce it during the visit, according to some reports.

Though his aides and some Republican lawmakers have cautioned against it, saying it will be challenged in courts, the US...