Rep. Ann Kirkpatrick became the fourth Arizona Democrat to back opening an impeachment inquiry against President Donald Trump, leaving only one member of her party in Arizona unclear on the matter.

During a speech on the floor of the House of Representatives on Tuesday, Kirkpatrick argued that the administration's decision to resist subpoenas from the House of Representatives leaves no alternative.

"I have a responsibility as a congresswoman, former prosecutor, and American citizen to stand up for the rule of law," she said. "After countless conversations with my constituents, after speaking with legal scholars and experts, after reviewing the Mueller report and after seeing administration officials defy congressional subpoenas, I’ve come to the conclusion that the House of Representatives must open an impeachment inquiry on President Donald Trump."

Rep. Tom O'Halleran, D-Ariz., is now the only Democrat from the state's U.S. House contingent who has not publicly joined the call for an impeachment inquiry. Trump narrowly carried O'Halleran's 1st Congressional District in 2016.

Last week, Rep. Ruben Gallego, D-Ariz., explained his support for an impeachment inquiry. In May, Rep. Greg Stanton, D-Ariz., did.

Rep. Raúl Grijalva, D-Ariz., supported a 2017 resolution to open impeachment proceedings against Trump and skipped his inaugural.

House Republicans, including all four from Arizona, have remained opposed to such a move.

Their support for Trump is expected to be tested again later Tuesday when Democrats are scheduled to vote on a resolution denouncing Trump's racist tweets Sunday telling four minority Democratic women to "go back and help fix the totally broken and crime infested places from which they came."

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Kirkpatrick's support for an impeachment inquiry brings her full circle on the issue. She seemed supportive of the idea in a secret recording last year while running in a competitive Democratic primary, then said she would be guided by what investigations such as the one led by former special counsel Robert Mueller found.

"Following Mueller’s alarming report, it is our job as a Congress to conduct oversight and deliver answers to the American people. Unfortunately, the president has called his administration to break the law and ignore our congressional subpoenas," Kirkpatrick said Tuesday. "Now we have no choice but to open an impeachment inquiry. This should not be a partisan fight or a debate about election strategy. It’s about the rule of law."

Kirkpatrick acknowledged "impeachment is risky. But allowing this president to defy the law is even more risky. If we don’t act now, our democracy may be threatened for years to come."

National Republicans hoping to unseat Kirkpatrick in the 2nd Congressional District suggested that Kirkpatrick's support for an impeachment inquiry came as no surprise to them.

“Ann Kirkpatrick is a socialist Democrat whose blind hatred of President Trump impacts her ability to do her job," Torunn Sinclair, a National Republican Congressional Committee spokeswoman, said in a written statement.

Reach the reporter Ronald J. Hansen at ronald.hansen@arizonarepublic.com or 602-444-4493. Follow him on Twitter @ronaldjhansen.