A clear majority of Americans now support the impeachment inquiry into Donald Trump, according to a new poll. Even among Republicans, support for the inquiry has jumped 21 points since July.

The Washington Post-Schar School poll released on Tuesday shows 58% support for the impeachment inquiry being conducted by Democrats in the House of Representatives, with 38% against.

Almost half of those polled, 49%, said the House should impeach Trump and recommend that he be removed from office.

According to the newspaper, “previous Post-Schar School or Post-ABC News polls taken … this year found majorities of Americans opposing the start of an impeachment proceeding, with 37% to 41% saying they favoured such a step.

“The recent revelations appear to have prompted many Americans to rethink their position.”

An average of impeachment polls conducted by the website fivethirtyeight.com puts national support for impeachment at a little over 48% and opposition close to 44%.

The “recent revelations” driving public opinion are centered around Trump’s conduct towards the leader of Ukraine, Volodymyr Zelinskiy, particularly a 25 July phone call in which the US president sought to have his opposite number investigate Joe Biden, a likely rival for the White House, over unsubstantiated allegations of corruption.

The motivation for a temporary freezing of military aid to Ukraine, mandated by Trump, is also in question. In the Post-Schar School poll, 58% of respondents said the freezing of aid mattered when judging Trump’s conduct.

The furious partisan fight over impeachment intensified on Tuesday when the Trump administration blocked the US ambassador to the EU Gordon Sondland from testifying to House Democrats in private.

WhatsApp messages released to Congress show Sondland and the Ukraine special envoy, Kurt Volker, who recently resigned that post, were involved in attempts to manage Trump’s pressure on Zelinskiy.

Trump said on Twitter Sondland had been prevented from appearing before “a totally compromised kangaroo court where Republican’s rights have been taken away, and true facts are not allowed out for the public”.

But the Post also pointed out indications that partisan attitudes to impeachment are shifting.

Nearly 80% of Democratic respondents now want Trump removed from office. Nearly 30% of Republicans support the impeachment inquiry, with nearly 20% favouring formal impeachment.

Independent support for the impeachment inquiry, a key factor, is at 57%, with 49% saying the House should vote to remove Trump from office.

Some Senate Republicans have criticised Trump’s behaviour over Ukraine but the upper chamber remains highly unlikely to convict the president should it be asked to do so.

Offering its “five takes from early polls on impeachment”, the Brookings Institution thinktank wrote: “Although the past two weeks have shifted the political terrain … the Democrats continue to face high odds against succeeding, and there is no guarantee that a failed effort to remove the president from office will serve their electoral interests.”