Robert wakes up one day to find digging machines and a work crew in his front yard, about to dig up his flower bed so they can widen the street. The workers tell him that the city has declared that it now owns those two meters of land, and that it will use them to widen the road running past Robert's house. A city lawyer shows up and gives Robert a check for $5,000 and apologizes for not giving him any advanced notice that the city would be taking his land; she also tells him that he cannot go to court to challenge the taking and that the matter is completely over and done with.

Robert doesn't want to give up his land, so he calls a lawyer. The lawyer tells him that the payment is above market value for the land, and that a court will almost certainly agree that it is just compensation. He also says that it's probably too late to ask for more, because the city has already taken the land; they were supposed to let him know about the taking in advance, so he could challenge it in court if he wanted to, but apparently someone made a mistake.

Is Robert more likely to be able to challenge this under the Fifth Amendment or the Fourteenth Amendment? In just a few words, why?