U.S. Sen. Mark Kelly (D-Ariz.) said Monday he will not be silenced or intimidated by the Trump administrations investigation into him over a video urging military members to ignore what Democratic lawmakers describe as unlawful orders.

Donald Trump has had one political play: bullying his opponents into silence, Kelly said at a press conference. He did it as a failed casino owner who bankrupted his properties and screwed over his contractors. He did it as a reality TV host known for firing people. And hes done it as president, who tries every day to intimidate people with no regard for the rights or well-being of the American people.

"I'll say this for the guy, while he's never seemed to do much right, for most of Donald Trump's career, bullying has worked out for him," Kelly added. "But not now, because I won't let it happen."

WATCH | Sen. Kelly accuses Trump of 'bullying' him into silence

Sen. Kelly accuses Trump of 'bullying' him into silence

Kelly's comments come a week after the Pentagon announced it had opened an investigation into him for serious allegations of misconduct. Officials did not say what the allegations involve.

IN CASE YOU MISSED IT | Pentagon opens investigation into Sen. Mark Kelly over misconduct allegations

The announcement followed the release of a video featuring Kelly and other Democrats, who urged service members to refuse unlawful orders after expressing concerns over U.S. military strikes on boats suspected of smuggling drugs in the Caribbean. The message did not cite specific examples or say where such orders might originate.

Republicans, including President Donald Trump, sharply criticized the video, accusing the lawmakers of encouraging the military to defy the commander in chief.

This is really bad, and Dangerous to our Country. Their words cannot be allowed to stand. SEDITIOUS BEHAVIOR FROM TRAITORS!!! LOCK THEM UP??? Trump wrote on his Truth Social platform.

Kelly, a former Navy pilot and NASA astronaut elected to the Senate in 2020, said the investigation would not deter him from fulfilling his duties. Under the Uniform Code of Military Justice, Kelly could be recalled to active duty for a possible court-martial or face administrative action.

ADDITIONAL REPORTING | White House says Trump wasn't calling for executions after condemning Democrats' military video

Monday marks a major milestone in American military history as the U.S. Marine Corps celebrates its 250th birthday and events honoring Marines past and present are planned across several states.

Birth of the Corps

The branch traces its origins to Nov. 10, 1775, when John Adams drafted a resolution creating the Continental Marines to serve alongside the Continental Navy in the Revolutionary War. Recruitment began at a brewery in Philadelphia, which is now recognized as the Corps' birthplace.

First Missions

The Marines' first assault came in the Bahamas in 1776, when they seized gunpowder and munitions from British soldiers. Throughout the Revolutionary War, Marines fought both at sea and on land, with historic clashes that helped secure American independence. The Continental Marines were then disbanded in 1783 after the war ended.

Re-establishment and 19th-century conflicts

The Marine Corps was eventually revived 15 years later to safeguard U.S. operations during a quasi-war against France, which landed them in Santo Domingo, Dominican Republic. The branch later took part in the War of 1812, the Mexican-American War, as well as various smaller wars defending U.S. interests around the world.

World War I "Devil Dogs"

During World War I, the Marine Corps deployed to battlefields in France, where heroic actions by the 4th Marine Brigade earned it the title of "Devil Dogs." Aviation also played a large role in the war effort, as Marine pilots flew bomber missions over Belgium and France.

World War II Mastering amphibious warfare

Between 1941 and 1945, the Marine Corps carried out various large-scale amphibious assaults across the Pacific Ocean, including historic battles in Guam, Okinawa, and Iwo Jima, which birthed the historic flag-raising photograph. By the end of the war, the branch had grown to six divisions, including five air wings, as well as its supporting troops.

Cold War era Korea and Vietnam

During the Korean War, U.S. Marines proved amphibious assault was still viable as they distinguished themselves in battles through harsh winter conditions, including at the Chosin Reservoir, where forces were able to hold against Chinese Communists in sub-zero temperatures.

Marine involvement in Vietnam expanded significantly in the mid-1960s. After the Tet Offensive in 1968, the Marine presence grew to a peak of about 85,000 troops. The drawdown began the following year, as South Vietnamese forces assumed a greater share of the fighting. Most Marine ground units had withdrawn by 1971, though Marines later returned to assist in the evacuation of U.S. personnel and civilians in Vietnam and neighboring Cambodia.

Post-Vietnam to modernization

In the years following, the Marine Corps shifted its focus to modernizing equipment and transforming readiness, while also providing support for various non-combative and humanitarian operations. It was during this period that Marines conducted peacekeeping and combat operations in places like Beirut, Lebanon. Marines also took part in a short but successful intervention in Granada.

Additionally, as the 1980s came to a close, Marines were summoned to respond to instability in Central America, where Operation Just Cause was launched in Panama to protect Americans and restore democracy. Then, in 1990, Iraq's invasion of Kuwait prompted what is deemed the largest deployment of Marine Corps forces since World War II. More than 90,000 troops were deployed to the Persian Gulf ahead of Operation Desert Storm the air campaign that began in 1991.

Post-9/11 Operations

Following the September 11, 2001, terrorist attacks on the U.S., Marines were rapidly deployed to Afghanistan, where they helped launch Operation Enduring Freedom then-President George W. Bush's global war on terror. Marines were also sent into Iraq, which led to high-stakes urban fighting in places like Fallujah, which is widely considered home to the most intense Marine battles since Vietnam.

The Corps has since carried out counterinsurgency operations, helped to train allied forces in the region, and supported humanitarian relief efforts. Marines also assisted in search and rescue efforts in Louisiana and Mississippi following Hurricanes Katrina and Rita.

Traditions and today's Corps

It was in 1921 that Major General Commandant John A. Lejeune officially proclaimed Nov. 10 as the official annual celebration of the founding of the U.S. Marine Corps. Each year, celebrations are held across the U.S. to honor all former and current Marines. Today's Marine Corps stands by its long and proud history of service to the nation, while maintaining readiness to respond to any potential challenges. The Corps' official motto is "Semper Fidelis," which is Latin for "Always Faithful."

Citing the successful nature of his tariffs imposed on foreign trade partners, U.S. President Donald Trump said Sunday the revenue raised by those import taxes will be used to pay down the national debt, invest in the U.S., and send direct payments to Americans.

"People that are against Tariffs are FOOLS!" the president wrote on his Truth Social platform. "We are now the Richest, Most Respected Country In the World, With Almost No Inflation, and A Record Stock Market Price. 401ks are Highest EVER."

ADDITIONAL REPORTING | What happens to revenue brought in by Trump's tariffs?

"We are taking in Trillions of Dollars and will soon begin paying down our ENORMOUS DEBT, $37 Trillion," President Trump added. "Record investment in the USA, plants and factories going up all over the place. A dividend of at least $2000 a person (not including high income people!) will be paid to everyone."

According to a September report from the Treasury Department, a total of $195 billion in customs duties were brought in during the first three quarters of the fiscal year. But since President Trump imposed his sweeping tariff agenda earlier this year, some companies have passed on tariff costs to consumers.

This also isn't the first time someone has proposed the idea of directing tariff revenue back to American citizens who face rising costs. Earlier this year, Sen. Josh Hawley (R-Mo.) introduced a bill titled the American Worker Rebate Act, also advocating for a share of the record tariff revenue to go directly to the American people.

RELATED STORY | Supreme Court appears skeptical of Trumps use of emergency powers for tariffs

Hawley's proposal suggests that $600 per adult and child should be deposited by the Treasury Department into qualifying bank accounts. To be eligible, individuals must earn under $75,000 per year, and couples filing jointly must make under $150,000. Those with higher incomes would receive a reduced payout.

However, the bill has stalled, and with the federal government shutdown stretching into day 40 on Sunday, any action from Congress is unlikely until lawmakers can agree on a proposal to end the current impasse.