Ted Cruz, a Republican, represents Texas in the Senate, where he is a member of the Armed Services Committee.

No decision by an elected official is more serious than whether to send our armed forces into conflict. President Obama was right to seek Congress’s authorization to use military force against Syria. But having carefully considered the president’s substantive arguments, I am compelled to vote against the requested authorization.

I do not make this decision lightly. I want to support our commander in chief. I emphatically condemn Bashar al-Assad’s use of chemical weapons against his people, and all Americans mourn the loss of innocent lives in Syria’s civil war.

But I do not believe a limited airstrike, as proposed by the president, will lead to success or improve conditions in Syria. There are other actions we can and should take to confront this atrocity, starting with forcing a vote in the U.N. Security Council condemning Assad for this attack; doing so would unify the world against the regime and expose China’s and Russia’s support for this tyrant.

The president insists on using a military option, which I oppose for three reasons:

First, Assad’s actions, however deplorable, are not a direct threat to U.S. national security. Many bad actors on the world stage have, tragically, oppressed and killed their citizens, even using chemical weapons to do so. Unilaterally avenging humanitarian disaster, however, is well outside the traditional scope of U.S. military action.

Second, just because Assad is a murderous thug does not mean that the rebels opposing him are necessarily better. As of May, seven of the nine major rebel groups appeared to have significant ties to Islamists, some of whom may have links to al-Qaeda and other terrorists. Their presence and power have only increased, according to media reports. We should never give weapons to people who hate us, and the United States should not support or arm al-Qaeda terrorists.

Third, the potential for escalation is immense. Syria is in the midst of a sectarian civil war, born of centuries-old animosities. We have no clear ally in this ­Sunni-Shiite conflict, and any “limited” and “proportional” strike could quickly get out of control, imperiling our allies and forcing us into the civil war.

The president and his secretary of state have repeatedly said that Assad’s use of chemical weapons violates an “international norm.” They insist it is critical that we send a “message” to Assad that his behavior is unacceptable. But it is not the job of U.S. troops to police international norms or to send messages. Our men and women in uniform have signed up to defend America.

On the cusp of the anniversary of the Sept. 11, 2001, terrorist attacks, we should remember that radical Islamic fanatics have declared war on the United States and are determined to destroy our way of life. Although the president has said that the threat from radical Islamism has receded, the reality is that the threat remains.

This threat was active at Fort Hood, where a terrorist attacked our soldiers in 2009. It was active in Libya, where terrorists murdered our ambassador and three other Americans one year ago this week. It was active this spring in Boston, where two terrorists who self-radicalized on the Internet used pressure cookers to kill civilians.

Today, the threat is active in Syria, where jihadists have infiltrated the rebel groups while Hezbollah is supporting Assad, making the presence of chemical weapons in Syria ever more perilous. And it is active in Iran, a state sponsor of terrorism that seeks a nuclear bomb to wipe the United States and Israel off the map.

If the president’s proposed military strike against Assad succeeds, al-Qaeda could be strengthened and terrorists could seize control of Syria’s vast cache of chemical weapons.

U.S. military force should always advance our national security. Should we in the future have intelligence that al-Qaeda or Hezbollah is on the verge of acquiring chemical weapons or that Iran is nearing a nuclear breakout, I would support aggressive military action to prevent them from acquiring those weapons because the alternative is unacceptable: allowing Islamic extremists to acquire chemical or nuclear weapons that could be used to slaughter millions in New York or Los Angeles or London or Tel Aviv.

If such occasion arises, the United States must lead to defend its national security interests. No other country is capable of putting together a coalition of like-minded nations and leading the fight against tyranny. And our allies should be encouraged to join us because it is in their own interests.

Yet none of this is occurring now. The administration’s current policy is based on averting immediate risk and accommodating the international community, as is demonstrated by its proposed defense of international norms in Syria. This action fails to protect U.S. long-term national security interests. I cannot in good conscience support it.

The president has rightly sought the will of Congress and, through Congress, the American people; he should heed the verdict.