U.S. President Barack Obama will give a major nationally televised speech Wednesday evening to outline an expanded military and political effort to combat Islamic militants in Syria and Iraq, and urge Congress to quickly give him authority to arm moderate Syrian opposition forces fighting President Bashar Assad.

“Tonight you will hear from the President how the United States will pursue a comprehensive strategy to degrade and ultimately destroy ISIL, including U.S. military action and support for the forces combating ISIL on the ground — both the opposition in Syria and a new, inclusive Iraqi government,” a senior administration official said in a statement issued to reporters early Wednesday morning.

“The President will discuss how we are building a coalition of Allies and partners in the region and in the broader international community to support our efforts, and will talk about how we work with the Congress as a partner in these efforts.”

But administration officials said Obama will press forward with other elements of his plan without formal authorization from lawmakers. That could include wide-ranging airstrikes in Iraq and possibly in Syria. Other elements of Obama’s plan, which he was to lay out in a televised speech Wednesday night, included increased support for Iraqi security forces, as well as military and diplomatic commitments from partners in Europe, the Middle East and elsewhere.

The speech, to be given at 9 p.m. (01000 GMT), is rare because presidents seldom ask broadcast networks to clear time when the most Americans are watching TV, doing so only to address the most critical issues.

Earlier in the day, the president and vice president are expected to meet with members of the National Security Council.

The White House said Obama told lawmakers after an hour-long discussion with congressional leaders Tuesday that he “has the authority he needs to take action” against the Islamic State militants. The White House added that the president still would welcome action from Congress that would “aid the overall effort and demonstrate to the world that the United States is united in defeating the threat.”

“ISIS must be stopped,” U.S. Senate Majority Leader Harry Reid said in prepared remarks. “It must be destroyed.”

For Obama, a sustained U.S. intervention in the Middle East is at odds with the vision he had for the region when he ran for president on a pledge to end the war in Iraq, where the role of American fighting forces drew to a close nearly three years ago. The timing of his announcement Wednesday night was all the more striking, scheduled just hours before anniversary commemorations of the terrorist attacks of Sept. 11, 2001.

Among the president’s most urgent priorities will be seeking authorization from Congress to arm more moderate elements of the opposition fighting Syrian President Bashar Assad. The president asked lawmakers earlier this year for a $500 million train-and-equip program, but the plan stalled in Congress.

The U.S. already has been running a smaller CIA program to train the rebels, but Obama is seeking approval for a more overt military effort that could involve staging training locations in countries near Syria.

With Obama ruling out sending U.S. ground troops into combat in Iraq or Syria, bolstering the capacity of the Iraqi security forces and Syrian opposition will be crucial to efforts to root out the Islamic State militant group, which has moved freely across the blurred border between the two countries. U.S. airstrikes could help give the forces in both countries the space to make gains against the extremists.

Administration officials said Obama also sees a congressional authorization for a Syrian train-and-equip message as sending a strong signal to allies who are considering similar efforts. Secretary of State John Kerry was traveling to the region for discussions in Saudi Arabia and Jordan.

The U.S. is already launching airstrikes against Islamic State targets inside Iraq, a mission undertaken at the invitation of the Iraqi government and without formal authorization from Congress. But the scope of the mission has been relatively limited to strikes that help protect American interests in the region and prevent humanitarian crises.

U.S. officials said Obama was expected to loosen those limitations and open a broader counterterrorism campaign against the militants in Iraq. And following the group’s shocking beheading of two American journalists in Syria, Obama began more seriously considering extending strikes into Syria.

People who have spoken with Obama in recent days said it appeared likely he would take that step. At a private dinner Monday with foreign policy experts, Obama emphasized the importance of viewing the Islamic State as one organization, not two groups separated by a border.

Administration officials and others familiar with Obama’s thinking spoke on condition of anonymity because they were not authorized to be identified.

Obama’s spokesman has said the president is willing “to go wherever is necessary to strike those who are threatening Americans.” However, Obama has continued to rule out sending U.S. troops into ground combat operations in the Middle East.

Germany has decided to send assault rifles, ammunition, anti-tank weapons and armored vehicles to Kurdish forces in Iraq fighting the Islamic State, breaking with Berlin’s previous reluctance to send weapons into conflicts. The deliveries haven’t started, but last week Germany sent a first planeload of military equipment such as helmets, protective vests, field glasses and mine-searching devices to Iraq.

In Congress, there was little consensus on the scope of Obama’s authority to broaden the campaign against the Islamic State extremists. While some lawmakers said the president has the power he needs under the Constitution, others were seeking a more central congressional role in the effort.

“I think it is to his advantage and the country’s advantage to have Congress buy into that,” Senate Minority Leader Mitch McConnell said before joining other Republican and Democratic leaders in the Oval Office on Tuesday for a meeting with Obama.

None of the leaders spoke to reporters as they left the White House.

However, an aide to House of Representatives Speaker John Boehner said the Ohio Republican expressed support for efforts to increase the effectiveness of the Iraqi security forces and for equipping the Syrian opposition. Boehner also said he would support the deployment of U.S. military personnel to Iraq in a training and advisory role and to “assist with lethal targeting” of Islamic State leadership, according to the aide, who spoke only on condition of anonymity because he was not authorized to discuss the private meeting by name.

In a shift for a war-weary nation, new polls suggest the American people would support a sustained air campaign. A Washington Post-ABC News poll released Monday showed 71 percent of Americans support airstrikes in Iraq, up from 54 percent just three weeks ago. And 65 percent say they support extending airstrikes into Syria.

Taking that latter step would raise legal and geopolitical issues that Obama has long sought to avoid, particularly without formal congressional authorization.

Unlike in Iraq, Obama would not be acting at the invitation of a host government. However, some international law experts say airstrikes could be justified as a matter of self-defense if Obama argues the Islamic State group poses a threat to the U.S. and its allies from inside Syria, whose government is unwilling or unable to stop it.

Another possibility: Although the U.S. has said it will not coordinate with Assad, his government could give back-channel consent to American attacks.

Obama would still have to contend with the notion that American airstrikes against the Islamic State militants were actually helping Assad, who has overseen Syria’s bloody civil war. The U.S. has long called for Assad to leave power, and the Islamic State group is one of the groups inside Syria that is seeking to oust him.

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Article based on reporting by The Associated Press, press office releases, and administration correspondence.