Editor's note: Sen. Marco Rubio, a Republican from Florida, is a member of the Senate Foreign Relations and Intelligence Committees. The opinions expressed in this commentary are solely those of the author.

(CNN) -- As the terrorist group the Islamic State of Iraq and Syria (ISIS) continues to capture and control more territory in Iraq and Syria, it is important to realize what is at stake in the region and for the American people.

The challenge that ISIS poses is not just to Iraq's stability but also to U.S. security. ISIS is a terrorist group with their own army and bank account that has a clear and growing ability to conduct terrorist attacks against the Iraqi government, Americans and U.S. interests, and even the U.S. homeland.

ISIS, although loosely affiliated with al Qaeda, is in many respects even more extreme in its methods and its brutality than the terrorists who plotted and carried out 9/11.

Although until now ISIS has focused its military goals on Syria and Iraq, its ranks include thousands of jihadists who have streamed into Syria and now into Iraq from around the globe as well as known terrorists who have been released or freed from Iraqi prisons.

ISIS's goal is to secure its hold over large swathes of territory in Syria and Iraq, to establish an Islamic state or "caliphate" that stretches across the heart of the Middle East.

As we have learned in the past, terrorists seek safe havens from which to operate, often in failed or failing states. They use this territory to train and equip themselves, raise funds and plot attacks.

In addition to the threat to the U.S. homeland, we also need to be concerned that if Iraq begins to fragment, the resulting chaos and instability will ripple throughout the region.

ISIS has sown incredible instability in Syria and is now seeking to do the same in Iraq. If we allow ISIS to spread further, their next targets will be U.S. allies and partners already under sufficient strain from the ongoing conflict in Syria, such as Jordan and even Saudi Arabia.

We have an imperfect partner in Iraqi Prime Minister Nuri al-Maliki, who has shown himself unable to govern inclusively. We need to make clear to Baghdad that significant U.S. assistance will not be possible unless a national unity government is formed that does not include al-Maliki.

Iran has already entered the fight on behalf of the al-Maliki government in Baghdad. But if we delegate this problem to Iran, we are likely to see the creation of a Shiite rump state that would effectively become an Iranian proxy and extend Iran's reach and influence from the Gulf of Oman to the Mediterranean Sea.

So, what should we do?

First and foremost, we need to move now to degrade ISIS's capabilities. The President's decision to send 300 advisers to Iraq is a good first step, but their ability to deter ISIS will be limited unless we eventually engage in airstrikes to target their leaders as well as the supply lines that they use to transfer weapons and fighters between Syria and Iraq. We know where these supply lines are, we should not hesitate to halt the ISIS resupply to their strongholds in Anbar, Ninawa and Salah ad-Din.

Second, we also need to understand that our lack of an effective Syria strategy has allowed ISIS to take hold and flourish in the region.

ISIS has been able to develop its capabilities, increase its ranks, and obtain combat experience for its fighters over the last 18 months in northern Syria.

We need to begin to tackle the root causes of the problem in Syria by overtly arming the moderate Syrian rebels that are fighting ISIS in that country even as we simultaneously tackle the challenge they currently pose to Iraq.

The U.S. and allies should consider additional counter terrorism measures in Syria, perhaps working with regional partners. This is all a response to the same problem, and must be part of a unified strategy.

The President's long overdue announcement on Thursday of an overt plan to train and equip moderates in the opposition is a welcome development, but we need to do much more to finally deal with the threat that the Syrian conflict poses to regional stability and ultimately, to U.S. security.

Third, as ISIS has gained ground in Iraq, its wealth and ability to make money have increased. We need to stop their ability to sell the Syrian and Iraqi oil they attempt to market to the outside world. We also need a new diplomatic strategy to counter ISIS funding and support.

Unfortunately, some of our partners in the Gulf have contributed to this problem. Others in the region have turned a blind eye to foreign fighters flocking to the fight. This needs to end.

Finally, our partners in the region need our support. Jordan deserves special attention and assistance. Jordan is already dealing with an influx of hundreds of thousands of refugees from the conflict in Syria. Jordan is a close partner of the United States and a likely target of ISIS's attention. In recent days, the group captured the border crossing between Iraq and Jordan.

The United States should find ways to make clear that the United States will defend Jordan's security, including militarily if necessary.

Some will argue that the challenges faced by Iraq or countries such as Jordan are none of our business. That we have spent too many years, lives, and dollars trying to make Iraq and the broader Middle East a better place.

None of the options before us are ideal, but the question is whether we take action against ISIS now or deal with the consequences later here on U.S. soil.

The stakes are too high for us to continue to ignore this problem.

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