The reports that President Donald Trump tried pressuring Ukraine into probing former Vice President Joe Biden, a leading Democrtic candidate for president, and his son, Hunter, struck Washington like an earthquake this week.

House Speaker Nancy Pelosi on Tuesday launched the nation's fourth-ever set of impeachment proceedings against a sitting president.

Senate Republicans, however, have mostly closed ranks around the president, either defending him or shrugging away concerns that Trump may have abused his power for his own gain.

Barring any more significant revelations that scramble their political calculations, GOP senators are unlikely to support impeaching a president who still commands a sky-high approval rating among Republican voters.

Fewer than a handful of GOP senators raised concerns over Trump's interactions with Ukraine, highlighting their desire to evade his political fury for real or perceived slights.

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The reports that President Donald Trump tried pressuring Ukraine into probing former Vice President Joe Biden, a leading Democrtic candidate for president, and his son, Hunter, struck Washington like an earthquake this week.

And it spurred House Speaker Nancy Pelosi on Tuesday to launch the nation's fourth-ever set of impeachment proceedings against a sitting president.

Senate Republicans, however, have mostly closed ranks around the president, either defending him or shrugging away concerns that Trump may have abused his power for his own gain.

Read more: Here are all the documents that lay out the allegations in the Trump-Ukraine scandal

And barring any more significant revelations that scramble their political calculations, GOP senators are unlikely to support impeaching a president who still commands a sky-high approval rating among Republican voters.

Fewer than a handful of GOP senators raised concerns over Trump's interactions with Ukraine, underscoring their desire to evade his political fury for real or perceived slights. At least 20 Republican senators would have to join all 45 Democrats and two independents to convict and oust Trump from office if an impeachment trial occurs.

Some GOP senators were reportedly stunned in private on Wednesday after the Trump administration released a rough transcript of a July 25 phone call between Trump and Ukrainian president Volodomyr Zelensky. It showed Trump asking Zelensky to work alongside Attorney General Bill Barr to investigate Biden's past conduct in the country. Trump also offered to meet with Zelensky at the White House after he promised to conduct such an inquiry.

Read more: The White House has a complete transcript of Ukraine call but hid it in a possible abuse of power, whistleblower complaint says

The transcript — combined with the disclosure of a whistleblower complaint filed against Trump from an officer at the Central Intelligence Agency — transformed the political debate around impeachment in only a few days. It also raised some alarm on Capitol Hill.

"Clearly what we've seen from the transcript itself is deeply troubling," Sen. Mitt Romney of Utah told reporters on Tuesday. And Sen. Ben Sasse of Nebraska said Republicans "ought not to be rushing to circle the wagons and say there's no 'there' there when there's obviously a lot that's very troubling there."

Sen. Mitt Romney of Utah. Bill Clark/CQ Roll Call

Most Republicans, though, have staunchly defended Trump in public against the impeachment proceedings and accused Democrats of overreach. Sen. Ted Cruz of Texas went on Fox News Friday to blast the inquiry as "just about attacking the president." House Majority Leader Sen. Mitch McConnell told Politico that it is "laughable to think this is anywhere close to an impeachable offense."

Still, Republicans are aware that more damaging information on Trump may come out in the coming months, and the proceedings casted a cloud of uncertainty on its impact on public opinion heading into the 2020 presidential election.

Read more: A timeline of Trump's campaign to pressure Ukraine's president into investigating Joe Biden

"Our sense is that it is still much too early to tell what the political impact of all of this is going to be," one Republican strategist with Senate campaign experience told the Wall Street Journal. "Everyone's going to be watching over the coming weeks to see how the numbers on impeachment move in public polling. I think particularly how independents see it."

Among Republican voters, Trump commands a 91% approval rating, according to a Gallup poll taken earlier this month before the Ukraine scandal erupted. But there are indications the impeachment proceedings are starting to sway the public — and that's one of the biggest factors determining whether Senate Republicans turn against the president.

Read more: Republican support for impeaching Trump doubled in the past few days amid escalating Ukraine scandal

Polling from Morning Consult released Thursday showed a nine-point spike in support for impeachment proceedings against Trump after only a few days, bringing it to 44% among all voters. There was also a six-point jump favoring impeachment among independents, while the figure of support among Republicans doubled to ten percent.

Just over half of Americans backed the launch of an impeachment inquiry againt Trump in a new Insider poll released Thursday, though they worried about the political repercussions of proceedings that could further split a divided nation among partisan lines.

That rising support also hinges on how the proceedings are carried out in the House. Democrats are eyeing a rapid investigation to capitalize on public outrage against Trump over Ukraine and hold a House vote on articles of impeachment around Thanksgiving, according to the Washington Post. But that strategy risks backfiring on them if it appears rushed.

Whether the impeachment proceedings continue to draw additional public support remains unclear, given the last one occurred over two decades ago before the advent of the internet and social media. But Senate Republicans will be keeping a close eye on how Trump's impeachment plays out among a public that's already been bombarded with Trump-related controversies for two years.