AZ-Sen: Former vice president Joe Biden endorses Democrat Kyrsten Sinema for Arizona US Senate

Former Vice President Joe Biden has endorsed Arizona Democrat Kyrsten Sinema in the high-profile U.S. Senate race to replace retiring Republican Sen. Jeff Flake, according to published reports.

Biden, viewed by some as a potential 2020 presidential candidate, called the U.S. congresswoman “as hard-working and principled as they come” in an announcement by the Sinema campaign.

The Arizona seat is seen by Democrats as a key to their plan to gain control of the Senate. Republicans currently dominate the chamber 51-49. Eight seats are up for election, including Flake’s.

What did Biden say?

“I am proud to support my friend Kyrsten Sinema in her campaign for Senate,” Biden said in the release. “Kyrsten understands the challenges and opportunities that Arizona families face every day and will make a great senator.”

Sinema told media she was honored to have Biden endorse her. The two worked together on the reauthorization of the Violence Against Women Act in 2013. KTAR-FM reported. She was first elected to the House that same year.

"I’ve seen first hand how Kyrsten gets things done for Arizona," Biden’s endorsement said.

"She was indispensable to our work to strengthen the landmark Violence Against Women Act, and brought a unique perspective of someone who has worked in communities and schools," he added. "Together, with Kyrsten, we expanded protections against domestic abuse and sexual assault."

How is she faring overall?

In several recent polls, Sinema is leading each of the top Republican candidates.

Arizona voters polled by CBS News favored Sinema over U.S. Rep. Martha McSally by 41 percent to 34 percent. She also topped former Arizona state Sen. Kelli Ward 43-35, and former Maricopa County Sheriff Joe Arpaio 45-28.

Also, an NBC News/Marist poll released showed Sinema leading McSally 49-38, Ward 48-38 and Arpaio 57-32.

Sinema faces Phoenix attorney and activist Deedra Abboud in the August Democratic primary, but Abboud is not considered a serious threat.

Recent polls suggest McSally will most likely face Sinema in the November general election.

A Data Orbital survey released Monday showed that 38 percent of likely GOP voters favored McSally. Ward came in second with 23 percent and Arapaio had 17 percent.