Biden and Kelly have the edge in a new Monmouth poll of likely voters in Arizona.

Joseph R. Biden Jr. holds a four-point edge over President Trump among registered voters in Arizona, though that advantage fades when the sample focuses only on likely voters, according to a Monmouth University poll released Thursday.

When assuming relatively high turnout, the poll found that Mr. Biden had 48 percent support among likely voters while Mr. Trump had 46 percent. Under a low-turnout model, the candidates were evenly split at 47 percent each.

Looking at all registered voters, Mr. Biden was at 48 percent and Mr. Trump was at 44 percent. In all three scenarios, the differences were within the poll’s margin of error.

Mark Kelly, the Democratic Senate nominee, maintains his steady advantage over Senator Martha McSally, the Republican incumbent, according to the poll.