(CNN) A newly unearthed letter from 2016 shows that Republican senators pushed for reforms to Ukraine's prosecutor general's office and judiciary, echoing calls then-Vice President Joe Biden made at the time.

CNN's KFile found a February 2016 bipartisan letter signed by several Republican senators that urged then-Ukrainian President Petro Poroshenko to "press ahead with urgent reforms to the Prosecutor General's office and judiciary."

The letter shows that addressing corruption in Ukraine's Prosecutor General's office had bipartisan support in the US and further undercuts a baseless attack made by President Donald Trump and his allies that Biden pressured the Ukrainian government to fire then Prosecutor General Viktor Shokin to stop investigations into a Ukrainian natural gas company that his son, Hunter Biden, sat on the board of. There is no evidence of wrongdoing by either Joe or Hunter Biden, nor is it clear whether Hunter was under investigation at all.

Trump called the 2016 dismissal of the Ukrainian prosecutor "unfair" in his July 25 call to Ukrainian President Volodymyr Zelensky, saying, "A lot of people are talking about that, the way they shut your very good prosecutor down and you had some very bad people involved," according to the rough transcript of the phone call

The 2016 letter, sent by members of the Senate Ukraine Caucus, was signed by Republican Sens. Rob Portman, Mark Kirk and Ron Johnson, as well as Democratic Sens. Dick Durbin, Jeanne Shaheen, Chris Murphy, Sherrod Brown, and Richard Blumenthal and focused on longstanding issues of corruption in Ukraine and urged reforms of the government.

"Succeeding in these reforms will show Russian President Vladimir Putin that an independent, transparent and democratic Ukraine can and will succeed," the letter reads. "It also offers a stark alternative to the authoritarianism and oligarchic cronyism prevalent in Russia. As such, we respectfully ask that you address the serious concerns raised by Minister Abromavičius. We similarly urge you to press ahead with urgent reforms to the Prosecutor General's Office and judiciary. The unanimous adoption by the Cabinet of Ministers of the Basic Principles and Action Plan is a good step."

Kirk is no longer in Congress. But Johnson signed onto a letter with Iowa Sen. Chuck Grassley last week to Attorney General Bill Barr asking him to investigate, in part, allegations surrounding Biden and Ukraine. Johnson's office did not respond to a request for comment. Portman's office did not comment.

Ukraine's legislature voted to fire Shokin in March 2016, a month after the letter was sent.

The letter was posted on the website of Republican Sen. Rob Portman, who in a tweet the same day expressed US support for anti-corruption efforts in Ukraine.

"Ukraine's US friends stand w/#Ukraine in fight against corruption," Portman wrote . "Impt to continue progress progress made since #EuroMaidan."

In December of 2015, in a speech to Ukraine's parliament, Biden made similar calls for changes to the judiciary and the General Prosecutor's office.

"It's not enough to set up a new anti-corruption bureau and establish a special prosecutor fighting corruption," Biden said . "The Office of the General Prosecutor desperately needs reform. The judiciary should be overhauled."

Bi-partisan support for anti-corruption efforts and praise for Biden's work

A CNN KFile review of hearings in the House and Senate at the time also found bi-partisan concern for corruption in Ukraine from Republican members of Congress and praise for Biden's efforts from former members of George W. Bush's administration and an Obama administration official who is now a nominee for an ambassadorship in the Trump administration.

At a hearing in March 2016 on Ukrainian reforms , Tennessee Sen. Bob Corker, the Republican chair of the Committee who would one day become a top Trump critic within the GOP, raised concerns about corruption in Ukraine and said his hearing would delve into what pressure the U.S. could apply.

At the same hearing, John E. Herbst, a former Ambassador to Ukraine in the Bush administration and now director of the Atlantic Council's Eurasia Center, testified that there was widespread support for the removal of Sholkin and praised specifically praised Biden.

"While reform progress was substantial in 2015, it was not enough for many in civil society and at least some reformers in the Rada and the government. Critics focused on the absence of any real changes in the Procurator General's Office and in the judiciary and claimed that the president and prime minister were not interested in going after these major sources of corruption," he said. "Both institutions were known to facilitate corruption. They pointed to the failure of the government—through the Procurator General— to indict any major figures from the Yanukovych administration for corruption. They complained, too, that Procurator General Viktor Shokin was a compromised figure who had served as Procurator General in the Yanukovych Administration.

"By late fall of 2015, the EU and the United States joined the chorus of those seeking Mr. Shokin's removal as the start of an overall reform of the Procurator General's Office," he added. "US Vice President Joe Biden spoke publicly about this before and during his December visit to Kyiv; but Mr. Shokin remained in place."

Added Herbst, "Vice President Biden has been a great advocate for reform in Ukraine."

In a June 2016 hearing before the Subcommittee on Europe, Eurasia, and Emerging Threats of the Committee, Alina Romanowski, then the State Department's coordinator of US Assistance to Europe and Eurasia, Bureau of European and Eurasian Affairs, testified that, "in Ukraine, President Poroshenko and the Rada replaced a Prosecutor-General widely seen as corrupt."