Walker dropped out of the race on Sept. 21 after a dip in the polls following weak debate performances and doubtful donors. At the time, he urged other candidates to leave the race so that voters could coalesce around a candidate who could take down Trump.
"I encourage other Republican presidential candidates to consider doing the same, so the voters can focus on a limited number of candidates who can offer a positive, conservative alternative to the current front-runner," Walker said at the time.
Since then, however, only low-polling Louisiana Gov. Bobby Jindal has suspended his campaign; Texas Gov. Rick Perry dropped out before Walker.
Meanwhile, Trump continues to lead the GOP field with 29.3 percent, according to the RealClearPolitics average of national polls
The Wisconsin governor on Tuesday was critical of Trump’s latest proposal for a “total and complete shutdown” of all Muslims entering the country until elected leaders can “figure out what’s going on.”
"When we look at the very real concerns we have in the world when it comes to safety," Walker said, "our focus should be on ensuring the people coming into this country are safe, and it shouldn't be on what religion they are."