Every national GOP primary poll in the past month has agreed: Donald Trump is in first place. But first-place status in polls like these can prove fleeting — and even leads that last months can suddenly vanish. That's what happened in 2008 and 2012, as you can see in this graphic:
Trump has been in first place for about a month. Rick Perry's stay at the top of the polls in 2011 lasted about that long, and Newt Gingrich's slightly longer (five and a half weeks). So if the billionaire mogul remains at the top of the crowded field for just a bit longer, he'll be able to say he's outlasted them. But as the Giuliani and Clinton examples from 2008 show, even a national poll lead that lasts many months is no guarantee of victory.
Now, Trump has also taken the lead in both Iowa and New Hampshire, which none of the 2012 candidates or Giuliani managed to do (though Clinton did). But it's also been quite common for the eventual winner in those early states to emerge very late — like John Kerry in Iowa and New Hampshire in 2004, Barack Obama and Mike Huckabee in Iowa in 2008, John McCain in New Hampshire in 2008, and Rick Santorum in Iowa in 2012. The takeaway? It's still early, and a whole lot more can change as the campaign continues.