If you thought America had become hopelessly polarized along partisan lines, reactions to President Trump’s Syrian strikes would prove you wrong.

Some prominent Democrats supported Trump for deploying the military on humanitarian grounds, while some strict constitutionalist Republicans complained that the president struck hastily without asking for congressional authorization. People on the left and right are encouraged to see Trump put some distance between America and Russia … and people on the left and right question whether the Syrian government was really behind the chemical weapons attack against a rebel-held province.

Our two major parties have been ideologically purified in many ways. But when it comes to foreign policy, both are a jumble -- torn between interventionist and isolationist impulses, lacking consensus on basic objectives and often reacting through their respective partisan filters. Meanwhile, Trump’s 180-degree turn on Syria, spinning away from years of opposition to intervention, creates mass confusion as to how exactly Trump envisions his commander-in-chief role and America’s role in the world. With so much unsettled, our parties have an opportunity, if not an obligation, to redefine their foreign policy principles for an increasingly globalized world.

Intra-party foreign policy divides are nothing new. President McKinley’s 1898 imperialistic grab of the Philippines, driven by then-Assistant Secretary of the Navy Theodore Roosevelt, drove some of their fellow Republicans into the newly formed Anti-Imperialist League. In 1915, the isolationist Secretary of State William Jennings Bryan resigned in an audacious but ultimately futile attempt to stop President Wilson from expanding the military and renouncing any possibility of entering the Great War. Isolationist Republicans found themselves marginalized in their own party once Gen. Dwight D. Eisenhower snatched the 1952 presidential nomination away from Sen. Robert Taft.

But we have forgotten that parties often lack consensus on international matters because these fault lines became submerged in the Cold War. Republicans mostly became fervent anti-communists. Vietnam soured many Democrats on interventionism. For decades, you could largely get away with classifying Republicans as hawks and Democrats as doves.

This was oversimplification – for example, President Clinton led a bombing campaign in the former Yugoslavia that Republicans largely opposed. Still, Democrats often ran on the principle of exhaustive diplomacy and Republicans on robust military spending.

When the Soviet Union collapsed, the defining feature of the partisan fault line collapsed with it. Further blurring followed the major events of the George W. Bush presidency – 9/11 and the Iraq War. The attack by al-Qaeda prompted conservatives to replace communism with “radical Islamic terrorism” as a singular enemy around which to organize a national security strategy. But the twisted intelligence regarding weapons of mass destruction and the sectarian strife that followed the Iraq invasion damaged the credibility of the “neoconservative” wing of the party, giving fresh oxygen to libertarian Republicans who view using the military for “regime change” as another example of big government overreach.

On the Democratic side, Bush’s crude unilateralism turbocharged support for international alliances and diplomatic statecraft, propelling Barack Obama to the Oval Office. But Obama’s approach to counter-terrorism, heavily reliant on drones and special operations, exposed a Democratic divide between those who support taking out terrorists by military means and those who believe military means create more terrorists.

Also defying ideological labels is the matter of genocide prevention. Clinton acted to stop “ethnic cleansing” in Kosovo after standing idly by when it occurred in neighboring Bosnia. Clinton later expressed regret that he did not rally the world to prevent genocide in Sudan.

In contrast, Obama acted swiftly to organize a U.N.-supported military effort to prevent a genocide in Sudan’s neighbor Libya, ousting its longtime strongman Moammar Gaddafi in the process. But fears of empowering Islamic terrorist groups compelled Obama to refrain from supporting the ouster Syrian President Bashar al-Assad with anything more than indirect aid to rebels. And while he almost launched a military strike in response to the August 2013 Syrian chemical weapons attack, lack of support from members of Congress in both parties led to his fateful switch to a diplomatic track.

Obama’s dichotomous decisions greatly influenced both presidential nominees in the 2016 campaign. Hillary Clinton firmly planted herself in the interventionist camp – defending the Libyan operation and proposing a militarily enforced “no-fly zone” in Syria. Her humanitarian-based hawkishness has a long Democratic lineage, running through nearly every Democratic president since Wilson. But it created space on the left for Sen. Bernie Sanders. He criticized both stances – even saying the removal of Assad was “secondary” to defeating ISIS. He rallied a substantial dove vote, but that was not sufficient to claim his party’s nomination.

Over in the Republican primary, Trump’s nomination proved that maximum hawkishness no longer guarantees maximum votes. Like Clinton, most Republican candidates supported a “no-fiy zone” in Syria, a recalibration from when they withheld support for Obama’s request of Congress in 2013. But Sen. Ted Cruz still contended that “we have no business stickin' our nose in that civil war." And the eventual winner similarly said, “Let Syria and ISIS fight. Why do we care?” as well as “I don't like Assad at all, but Assad is killing ISIS”

Trump’s turn away from “regime change” didn’t exactly put him in the neo-isolationist libertarian camp. He pledged to “bomb the [expletive]” out of ISIS and was brazenly imperialistic when he lamented we didn’t “take the oil” after the Iraq War. Trump ran as a classic nationalist -- willing to fight, or not fight, depending on America’s narrow self-interest. Human rights or international norms would not be factoring in to his decisions.

On top of all that, Russia’s role in the 2016 election has further scrambled the alignment of the two parties.

In 2012, Obama famously slammed Mitt Romney’s focus on Russia with “the 1980s are now calling to ask for their foreign policy back.” It’s easy to mock Obama in hindsight, but it was understandable at the time. During Obama’s first term, the American relationship with Russia had taken a turn for the better. Then-President Dmitry Medvedev acquiesced on the U.N. resolution that approved military action in Libya and a seemingly sidelined Vladimir Putin was singing “Blueberry Hill” to Sharon Stone. Even in the second term, Russia cooperated with America to negotiate the Iran nuclear deal. But by 2016, Putin’s actions in Crimea and Syria made clear the attempted “reset” in our relationship had failed to turn Russia into an ally.

The postures of the parties flipped. Hillary Clinton was openly mistrustful of Putin during the 2016 campaign, while Trump was often complimentary. And the post-election revelations have turned many rank-and-file Democrats into born-again Cold War warriors. Among Republicans, some longtime Russia critics like Sen. John McCain remained steadfastly cynical, but others view the no-longer communist Russia as a useful partner in fighting “radical Islamic terrorism,” and set aside concerns about free elections and human rights.

Trump presumably still fits in the latter camp. But the strike against Russia’s client state is a reminder that he is mercurial and his foreign policy views likely are not deeply held. And the abruptly changing emphasis of Democrats and Republicans tells us that neither party has invested much intellectual capital into developing and articulating a foreign policy vision relevant to the myriad of challenges we face in the 21st century.

What it means to be a Democrat and what it means to be a Republican is changing before our eyes. As Trump learns on the job, party platforms will inevitably evolve in response. However, leaders in both parties would be wise to proactively develop and define their respective foreign policy philosophies. Doing so would not only help them influence a shallow and potentially malleable president, but it would also ensure their views are rooted in reality, and not political expediency.