On Friday, Donald Trump was sworn in as our 45th president and America's commander in chief. Like his predecessors, he will face a range of national security challenges. But unlike most previous presidents, President Trump will also have to confront a rapidly evolving terrorist threat. A threat that has grown ever more complex even over the last year given the influence of ISIS, lingering threats from al-Qaeda, and pockets of support for both worldwide - including in the United States.

Which is why I implore the president to keep three things in mind over the months ahead:

Be vigilant, especially in your first year.

Think outside the box, particularly when it comes to counterterrorism strategies.

Remember that nuance is key, throughout.

The transition of power in the Oval Office is a good moment to reiterate that America remains vulnerable, especially in the first few months of a new administration. Don't forget that three of the most significant terrorist attacks on U.S. soil occurred during the year of a presidential inauguration: Sept. 11, the November 2009 attack at Fort Hood, Texas, and the April 2013 Boston Marathon bombing remain watershed moments for America, whether measured in terms of fatalities, societal impact, or their lasting effect on our national security.

Yes, there have been other terrorist attacks or attempted attacks in America, particularly as online radicalization has proliferated and increased concerns for homegrown terrorism. But our country's vulnerabilities are amplified during the first few months of a presidency - when many of the new administration's security officials are still being selected, when freshly appointed officials are learning the ropes, and when cross-agency collaboration at senior levels hasn't yet gained traction.

While there are still countless civil servants and military officers working to protect us during these transitions - I was one myself in 2009, while serving as a counterterrorism adviser at the Treasury Department - it remains an especially important period to be vigilant for homegrown radicalization and terrorist incidents on U.S. soil.

For a new administration, it's likewise an important time to consider the role of innovation in one's overall strategy for combating terrorism, at home and abroad. In policymaker parlance, it's about using "every tool in the counterterrorism toolbox" - a pithy way of admitting the limitations of a purely militaristic approach to counterterrorism and leaving room for critical, alternative approaches to fighting such an asymmetric threat.

It's why the Bush administration greatly expanded the breadth of financial tools at its disposal, enhancing its approach to obstruct supporters of terrorism with targeted sanctions and devising new ways to thwart the flow of cash to terrorist organizations. It's why the Obama administration relied heavily on drone strikes and special operations, while also exploring novel approaches to countering terrorist propaganda online. And why our overseas partners, from Europe to the Middle East and beyond, continue to test new ways to deradicalize terrorists.

Even as the U.S. military will continue to play a pivotal role in our counterterrorism efforts, alternative tools - particularly those that leverage the latest technology and help civil society counter radicalization - will remain critical to any effective counterterrorism strategy. President Trump and his team must be open to fresh ideas in these areas to prevent further attacks.

Which brings us to the need for nuance - a central aspect of any president's approach to foreign policy and national security, but especially critical to effectively combat modern terrorism.

Over the last decade, we've seen our top terrorist threat shift from al-Qaeda to ISIS, from Pakistan and Afghanistan to Iraq and Syria. We've seen the internet and social media play an ever-greater role in radicalization, even as the root causes of terrorism remain hotly debated. There's still no simple answer to Guantanamo Bay's detention center, and no clear way to move past an era when terrorism is a top threat to American security. Complex threats like these require carefully calibrated approaches that employ a mix of prevention as well as reaction.

Ultimately, President Trump's success as our commander in chief will largely be measured on his ability to protect the homeland from a major terrorist attack - and, therefore, his administration's ability to stay vigilant early on, to embrace new counterterrorism strategies, and to favor nuanced tactics throughout. Counterterrorism policy is one area in which Americans of all political stripes must come together to help the new administration succeed.

Marisa Porges is head of school at the Baldwin School in Bryn Mawr and a former counterterrorism policy adviser in the Bush and Obama administrations.  mporges@baldwinschool.org