There are some problems with declaring this Trump bump something that is actually going to last until election day.First is that the Fox News and Rasmussen polls don't give you an exact breakdown of the demographic composition of the their sample, at least not in the publicly available versions of the reports, so it isn't possible to say if they are oversampling or undersampling White voters. This makes a pretty big difference. Blacks and Latinos and Asians are pretty solidly anti-Trump, so an electorate with the Demographics of 2014 as opposed to one that looks like 2012 is 3 points Whiter and therefore 1-2 points more Republican. Both Rasmussen and Fox News overestimated Romney support right up to the end in 2012 for this sort of sampling problem.Second, the writeup of the Rasmussen poll from May 2nd indicated that they are doing something very strange with their Likely Voter model. They say that they are explicitly asking people if they intend to "stay home" in November, find that this group would prefer Trump to Clinton, and are then declaring these people to be likely voters counted as Trump backers.Third, and most important, if you look at the details for all of the polls in the RCP average, they all agree that Clinton's loss in support is coming from Whites aged 18-29, more or less explicitly because they are angry that nominee isn't Sanders. These kids are, only just now, declaring Trump to be preferable to Clinton or abstaining from picking a side. The ABC News poll states this explicitly.So the race continuing to be a dead heat is extremely contingent on what percentage of these kids actually pull the lever for Trump (not very likely) stay home (a lot more likely) or are convinced by Sanders to vote for Clinton because he endorses her once it becomes obvious, even to him, that he's lost the nomination. (Still more likely than not.)Short version, this Trump surge is only likely to go on as long as Sanders is still campaigning.