Tucson Congresswoman Martha McSally leads the three-way Republican primary for U.S. Senate, while former Maricopa County Sheriff Joe Arpaio's entry into the race is hurting former state legislator Kelli Ward, according to a new poll released Tuesday.

The poll, by the Phoenix-based consulting firm Data Orbital, also shows President Donald Trump's popularity among Arizona Republican voters is higher than it was three months ago: His favorability rating is 74 percent, versus 71 percent in October.

Here is the breakdown on the U.S. Senate race to fill the seat being vacated by retiring Sen. Jeff Flake:

• McSally 31%

• Arpaio 22%

• Ward 19%

• Undecided 27%

Perhaps the most surprising finding in the poll is McSally leads Arpaio among Republican voters in Maricopa County, the state's largest county and Arpaio's home turf for the 24 years he was sheriff, until his 2016 defeat:

• McSally 28%

• Arpaio 22%

• Ward 21%

• Undecided 29%

“We have been tracking the race from the beginning and have seen numbers drastically fluctuate with each announcement," pollster George Khalaf said in a prepared statement.

"There was a lot of speculation regarding Kelli Ward's standing in the race following Sheriff Arpaio's announcement and it is clear his candidacy has hurt her drastically. With a little more than eight months to go, this race is long from over, but Congresswomen McSally seems to be out of the gate as an early leader."

The poll was conducted from January 11 to 15 among 500 likely primary election voters.

The 85-year-old Arpaio stunned the political world by entering the Senate race one week ago today. McSally announced her run last Friday.

Ward has been running for the Senate virtually non-stop for the last three years, losing to Sen. John McCain in the 2016 primary but entering the 2018 race shortly after the November 2016 election.

The all-live survey obtained 70 percent of the results from land line users and 30 percent from cell phone users.

The poll has has a margin of error at plus or minus 4.38 percent.