The death of a police officer from injuries sustained as President Donald Trump’s supporters stormed the Capitol is forcing hard questions about the defeated president’s remaining days in office and the ability of the Capitol Police to secure the area.

The US Capitol Police said in a statement that Officer Brian D. Sicknick was injured “while physically engaging with protesters” during the Wednesday riot.

He is the fifth person to die because of the melee.

During the melee, Mr Sicknick was hit in the head with a fire extinguisher, two law enforcement officials said.

The rampage that has shocked the world and left the country on edge forced the resignations of three top Capitol security officials over the failure to stop the breach.

It led politicians to demand a review of operations and an FBI briefing over what they called a “terrorist attack”.

And it is prompting a broader reckoning over Mr Trump’s tenure in office and what comes next for a torn nation.

Protesters were urged by Mr Trump during a rally near the White House earlier Wednesday to head to Capitol Hill, where politicians were scheduled to confirm Mr Biden’s presidential victory.

The mob swiftly broke through police barriers, smashed windows and paraded through the halls, sending politicians into hiding.

One protester, a white woman, was shot to death by Capitol Police, and there were dozens of arrests.

Three other people died after “medical emergencies” related to the breach.

Despite Mr Trump’s repeated claims of voter fraud, election officials and his own former attorney general have said there were no problems on a scale that would change the outcome.

All the states have certified their results as fair and accurate, by Republican and Democratic officials alike.

Senator Ben Sasse, a Republican, said news of the police officer’s death was “gut-wrenching”.

“None of this should have happened,” Mr Sasse said in a statement.

“Lord, have mercy.”

Mr Sicknick had returned to his division office after the incident and collapsed, the statement said.

He was taken to a local hospital where he died on Thursday.

Two House Democrats on committees overseeing the Capitol police budgets said those responsible need to be held to answer for the “senseless” death.

“We must ensure that the mob who attacked the People’s House and those who instigated them are held fully accountable,” said Rosa DeLauro and Tim Ryan in a statement.

Earlier Thursday, House Speaker Nancy Pelosi said any remaining day with the president in power could be “a horror show for America”.

Likewise, Senate Democratic leader Chuck Schumer said the attack on the Capitol was “an insurrection against the United States, incited by the president”, and Mr Trump must not stay in office “one day” longer.

Ms Pelosi and Mr Schumer called for invoking the 25th Amendment to the Constitution to force Mr Trump from office before President-elect Joe Biden is inaugurated on January 20.

Mr Schumer said he and Ms Pelosi tried to call Vice President Mike Pence early on Thursday to discuss that option but were unable to connect with him.

At least one Republican politician joined the effort.

The procedure allows for the vice president and a majority of the Cabinet to declare the president unfit for office.

The vice president then becomes acting president.

Ms Pelosi said if the president’s Cabinet does not swiftly act, the House may proceed to impeach Mr Trump.

Mr Trump, who had repeatedly refused to concede the election, did so in a late Thursday video from the White House vowing a “seamless transition of power”.

Two Republicans who led efforts to challenge the election results, Ted Cruz of Texas and Josh Hawley of Missouri, faced angry peers in the Senate.

Mr Cruz defended his objection to the election results as “the right thing to do” as he tried unsuccessfully to have Congress launch an investigation.

In the House, Republican leaders Representative Kevin McCarthy of California and Representative Steve Scalise of Louisiana joined in the failed effort to overturn Mr Biden’s win by objecting to the Electoral College results.

With tensions high, the Capitol shuttered and politicians not scheduled to return until the inauguration, an uneasy feeling of stalemate settled over a main seat of national power as Mr Trump remained holed up at the White House.