Rep. Martha McSally Martha Elizabeth McSallyThe Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' New ABC/WaPost poll finds Trump edging Biden in Arizona, Florida MORE (R-Ariz.) is the front-runner in Arizona’s heavily contested GOP Senate primary, but she still trails Rep. Kyrsten Sinema (D-Ariz.) in a hypothetical general election match-up, according to a new poll.

A poll conducted by Phoenix-based OH Predictive Insights (OHPI) has McSally ahead by 8 points over her toughest primary opponent, former state Sen. Kelli Ward (R), 35 percent to 27 percent. Former Maricopa County Sheriff Joe Arpaio is far behind in third, with 15 percent. Twenty-three percent of voters remain undecided going into Arizona’s primary on Aug. 28.

McSally’s lead over Ward dipped by 6 points since OHPI’s poll from mid-June. In the June poll, the congresswoman held a comfortable 14-point lead over Ward, who has kept up her heavy attacks on McSally related to President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE and immigration.

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“The Arizona Senate contest is tightening and expect the attacks to ramp up as we head closer to election day,” said Mike Noble, managing partner and chief pollster at OH Predictive Insights.

In a potential general election match-up, McSally still falls short against Sinema. The Democratic congresswoman holds a 4-point lead over McSally, 48 percent to 44 percent. And Sinema is ahead by double-digit margins when facing Ward and Arpaio in respective match-ups.

There’s some good news for McSally in the general election polling, since Sinema was leading by 6 points, 48 percent to 42 percent, in OHPI’s June poll.

Arizona’s race to replace retiring GOP Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE (Ariz.) is one of the top Senate races this cycle that can determine control of the majority.

Democrats haven’t won a Senate seat in Arizona since 1988, but they feel emboldened this year as their party’s likely nominee continues to outraise her GOP opponents and lead in the polls.

The poll was conducted from July 23-25 and surveyed 576 likely GOP primary voters. The margin of error for that sample was 4.08 percentage points.

For the general election sample, the poll was conducted from July 23-25 and surveyed 600 likely general election voters. The margin of error was 4 percentage points.