Reuters/Rick Wilking The president reiterated a variation of one of his key campaign promises on Sunday, tweeting that Mexico would pay for the wall Trump wants to build across the border between the southern United States and Mexico. "Eventually, but at a later date so we can get started early, Mexico will be paying, in some form, for the badly needed border wall," Trump tweeted. Trump also attacked Democrats in Congress who did not want to allocate US funding towards constructing the wall. "The Democrats don't want money from budget going to border wall despite the fact that it will stop drugs and very bad MS 13 gang members," he tweeted. Trump kicked off his presidential campaign in June 2015 by saying that Mexico would immediately pay for the border wall and repeated that throughout the election cycle.