Sen. Lindsey Graham warned about how "easy" it would have been for terrorists to enter the Capitol on Jan. 6, 2021, and said the security breach was "stunning" two decades after the 9/11 terrorist attacks.

Graham, R-S.C., said those in charge of Capitol security must be held accountable, just as the individuals who defiled the Capitol must be prosecuted.

"I still cannot believe a mob was able to take over the United States Capitol during such a pivotal moment – certifying a presidential election," Graham tweeted Thursday. "It would have been so easy for terrorists to boot strap onto this protest and wreak even further destruction on the U.S. Capitol.

WHAT THE JAN. 6 HOUSE COMMITTEE HAS BEEN UP TO: BY THE NUMBERS

"Regardless of the reason for the assault on the Capitol, to lose control in such a fashion 20 years after 9/11 is stunning," Graham added. 

Graham made the comments as part of a lengthy Twitter statement one year after the attack where he also took shots at President Biden's "failed policies" and "weak leadership."

BIDEN IN JAN. 6 SPEECH SHARPLY CRITICIZES TRUMP AS SPREADING 'WEB OF LIES,' STOKING RIOT

Biden made a speech at the Capitol earlier Thursday where he blamed former President Trump for stoking insurrection at the Capitol on Jan. 6, 2021, and spreading a "web of lies" in order to "prevent" the peaceful transfer of power during certification of the 2020 presidential election, blasting him as an individual who "sees his own interest as more important than America's." 

Sen. Lindsey Graham

Sen. Lindsey Graham, R-S.C. blasted President Biden's speech one year after the Capitol riot. (Fox News)

Graham accused Biden and Vice President Harris of trying to politicize the attack and use Jan. 6 to promote voting rights reform and changing the Senate filibuster to do so.

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"President Biden and Vice President Harris’s speeches today were an effort to resurrect a failed presidency more than marking the anniversary of a dark day in American history," Graham wrote. 

House and Senate Democratic leaders are holding a series of events at the Capitol to remember Jan. 6 and those who were injured or killed in the aftermath of the mob attack. 

Sen. Debbie Stabenow, D-Mich., said Thursday she regrets that more Republicans were not participating and called out Graham for first condemning the attack, but then reviving his relationship with former President Trump.

"Republicans said the right things that day," Stabenow said in a floor speech Thursday. "The senior senator from South Carolina said soon after the riot that he was humiliated and embarrassed for our country, and that Trump should ‘count him out.’ But a few short weeks later, Trump counted him in for two days of golf and dining at Mar-a-Lago."

Fox News' Brooke Singman contributed to this report.