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A Wednesday poll from The Arizona Republic showed Clinton with a 5-point lead over Donald Trump in a four-way race that included Libertarian nominee Gary Johnson and Green Party nominee Jill Stein.
The Democratic nominee held a 43% to 38% advantage over the Republican nominee in the poll.
In a late-August Arizona Republic poll, Clinton's lead over Trump was just 1 point.
After the poll's publication, Clinton swung into a slight lead in the RealClearPolitics polling average for the state. She now leads the Manhattan billionaire by 0.2 points.
The last Democrat to win a presidential race in Arizona was Clinton's husband, Bill, in 1996.
The poll's margin of error was 4.3 percentage points.