Sen. Rob Portman of Ohio is one of the few Republicans lawmakers to openly rebuke President Donald Trump for asking the new Ukrainian president in late July to investigate one of Trump’s major Democratic rivals, former vice president Joe Biden.

“The President should not have raised the Biden issue on that call, period,” Portman told on Monday. “It is not appropriate for a president to engage a foreign government in an investigation of a political opponent.”

The Few Republicans Calling for Probe of Whistleblower Complaint

Portman's views are a relative rarity among the 252 Republican members of Congress. show just 28% of Republican voters support the impeachment inquiry. Just a handful of sitting Republican lawmakers have spoken in support.

The Few Republicans Calling for Probe of Whistleblower Complaint

For the president to be impeached and removed from office, 20 out of 53 Republican senators would need to join with the Democrats and vote to remove him.

The Few Republicans Calling for Probe of Whistleblower Complaint

For Portman, that's a step too far for now.

Portman said despite his differences with Trump, who recently urged both Ukraine and China to investigate Biden, he did not view Trump’s conduct as an impeachable offense. Trump so far has commanded overwhelming Republican backing as he battles against the House Democrats’ impeachment inquiry that was sparked by the phone call between the U.S. and Ukrainian presidents.

However, a small but growing number of Republicans are favoring an investigation as more details of the scandal emerge, according to a VOA review.

Former Secretary of State Colin Powell, who served in Republican President George W. Bush’s administration, recently criticized the state of U.S. foreign policy and blamed Republicans for being “terrified” of criticizing Trump.

Powell said during a televised lecture moderated by CNN columnist Fareed Zakaria that “Republican leaders and members of the Congress . . . are holding back because they’re terrified of what will happen [to] any one of them if they speak out.” What they fear, he said, was losing their primary elections if Trump forces came after them. The four-star general suggested that losing a primary would not be “such a disaster.”

In all, about 16 prominent Republicans including Portman and Powell have publicly raised concern about Trump’s conduct or defended the House Democrats’ right to seek answers to questions about Trump’s efforts to enlist foreign countries to investigate Biden and his son, Hunter -- who did business in Ukraine and China during his father’s tenure as vice president. Here is a summary of the 14 other Republicans who have spoken out.

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The Nevada House member initially suggested that the impeachment inquiry is justified, but later pulled back. In a call with the Nevada Independent, Amodei stated he was “a big fan of oversight, so let’s let the committees get to work and see where it goes.” Later Amodei emphasized that “In no way, shape, or form, did I indicate support for impeachment.” He said that he would base his vote on whether he found “credible evidence” that Trump “broke a specific law.”

The Nebraska senator wrote to the after Trump suggested China investigate Joe Biden for corruption. “If the Biden kid broke laws by selling his name to Beijing, that’s a matter for American courts, not communist tyrants running torture camps,” Sasse wrote. The senator called the House Democrats’ impeachment inquiry a “partisan clown show.” In contrast, he said the Senate inquiry is “working to follow the facts one step at a time.” Sasse previously said the whistleblower complaint against Trump that triggered the impeachment probe contained "real troubling things" and that Republicans "ought not just circle the wagons." However, he has not made a judgment on whether Trump should be impeached.

The Maine senator took issue with Trump's comments on the White House lawn that China should investigate Biden for corruption. Collins said she had no comment on the current evidence for the impeachment inquiry. She said she hopes the impeachment inquiry will “be done with the seriousness that any impeachment proceeding deserves.” Collins said she was preparing for the likelihood that the House would send articles of impeachment to the Senate. Collins told thethat she plans to act as a juror as she did in the impeachment trial of President Bill Clinton in 1998.