WASHINGTON (NewsNation Now) — Nearly five months after being deployed to the U.S. Capitol to help quell the Jan. 6 insurrection, National Guard troops were set to leave and turn over security of the area to Capitol Police amid congressional debate over whether to form an independent bipartisan commission to investigate the attack.

Former President Donald Trump’s supporters stormed the building following a speech in which the then-president repeated unfounded claims that his November 2020 election defeat was the result of widespread voter fraud. Five people including a Capitol Police officer died in the violence.

Guard troops, their mission ending Sunday, were expected to be leaving on Monday, a person familiar with the plan told The Associated Press. The person was not authorized to discuss the plan by name and requested anonymity.

The Pentagon announced earlier in the week that an extension of the Guard presence — 2,149 troops — had not been requested.

The planned departure came as Democrats and Republicans sparred over how to fund fortifications of the Capitol and whether to form an independent bipartisan commission to investigate the riots.

Some Republican lawmakers have begun downplaying the event despite the handful of deaths, injuries to scores of police officers, hundreds of arrests, damages to the building and shouted threats against lawmakers from many of those who stormed the building. Much of the violence was caught on camera.

Democrats say an independent investigation is crucial to reckoning what happened that day. House Speaker Nancy Pelosi said that protecting the Capitol and the people who work inside it is of “the highest priority,” and that a commission is imperative “to examine and report upon the facts, causes and security relating to the terrorist mob attack.”

Modeled after the investigation into the Sept. 11, 2001, attacks, the legislation would establish an independent, 10-member commission that would make recommendations by the end of the year for securing the Capitol and preventing another insurrection.

The security spending bill would provide congressional offices with more money to combat those threats, including enhanced travel security, upgrades to home-district offices and better intelligence to track people down. The bill would also “harden” the complex by reinforcing doors and windows, adding security vestibules and cameras and providing dollars for removable fencing that could quickly be erected during a threatening situation while leaving the Capitol open to visitors.

The House on Thursday approved — by a single vote largely along party lines — a $1.9 billion measure to fortify the Capitol. The next day the House approved with 35 Republican votes the formation of an investigative commission. Both measures face an uncertain future in the evenly divided Senate.

Minority Leader Mitch McConnell, R-Ky., has said he opposes the commission proposal, which would need significant Republican support to advance under Senate rules. Republican opponents say the commission would become a political tool as midterms elections approach, though the proposal requires its work to be concluded by the end of this year.

Many Republicans in Congress have demanded the commission also investigate last summer’s protests against racism and police violence, including the Black Lives Matter movement, that were sparked by George Floyd’s murder in Minneapolis, an event unrelated to the insurrection at the Capitol.

The Associated Press contributed to this report.