Part of any impeachment fight is the fierce and sometimes memorable campaign to educate and sway public opinion. The Clinton impeachment, for example, exposed Americans to arcane debates about the meaning of the word “is.”

But today, while Americans are learning Latin phrases such as quid pro quo and hearing about the Founders’ intentions regarding impeachment, Democrats seem to be squandering a golden opportunity to convey something crucial: Ukraine is, and has always been, of the utmost strategic import, which means President Trump’s actions go beyond bribery or quid pro quos. He has been accused of trading U.S. security for his personal, political gain — the most flagrant of high crimes and misdemeanors.

On Thursday, Rep. Scott Perry (R-Pa.) called into question Ukraine’s strategic import, hinting the country’s value had been exaggerated by Democrats and “deep state” bureaucrats: “Okay, suddenly they’re a key strategic ally. I never heard that before the last eight weeks.”

Herein lies the problem. Ukraine’s supreme geostrategic and historical importance shouldn’t be in question, and it doesn’t have anything to do with partisan politics. It certainly didn’t during the Cold War or early post-Cold War eras. Politicians ranging from Dwight Eisenhower to Bill Clinton to John McCain all spoke publicly about the importance of Ukraine for U.S. national security. They understood, like statesmen and strategists had before them, that holding sway over its strategic territory, the pivotal buffer zone separating Western and Central Europe from Eastern Europe and Asia, was the key to becoming the trendsetting global power.

Halford Mackinder (the inventor of the discipline of geopolitics) postulated in 1904 that “Eurasia is the cockpit of world history and Ukraine is its pivot.”

Although the British establishment at the time viewed Germany as its primary adversary, Mackinder envisioned future geopolitical struggles would probably pit the West against Russia. He anticipated that whichever bloc dominated the grain fields, strategic highways and Black Sea ports of Ukraine would ultimately prevail.

The world started to glimpse the pivotal import of Ukraine when Tsarist Russia’s inability to hold Poland and Ukraine after their decisive early defeat at Tannenberg essentially knocked Russia out of the Great War, fomenting the domestic unrest that eventually led to the rise of the Soviet Union.

During the Russian Civil War (1918-1921) that followed, the French, British and Americans backed what were known as the White Russians, who opposed Communism and Lenin’s forces. Despite this Western support, once the White Russians lost Crimea — the peninsula that holds the nearest warm-weather port (Sevastopol) that is required to feed the Russian people, base its navy and fuel its economy — they succumbed.

Soviet control of Ukraine meant Communism would be Eastern and Central Europe’s (as well as Asia’s) dominant ideological force for the next 75 years. Hitler’s desire to use Ukraine as Lebensraum (living or buffering space) for the Aryan race was the primary reason he abandoned his nonaggression pact with Stalin. This crucial blunder, which necessitated fighting a two-front war, eventually cost the Nazis World War II.

During the Cold War, Soviet control of Ukraine connected it to the advanced economies of Central Europe and was essential for the Soviet Union to be a global power: Crimea was its industrial and naval transport link to the rest of the world, while Ukrainian grain and nuclear power plants fed and fueled Russia.

With the collapse of the Soviet Union, the United States became the world’s new hegemonic power, which gave it the opportunity to dominate Central Europe and Ukraine via a web of investment and security linkages.

Conversely, Russian Presidents Boris Yeltsin and later Vladimir Putin wanted to dominate Ukraine, believing Russia deserved a buffer zone — just as the czars and Soviets had before them. Western leaders disagreed, pushing for Ukraine’s participation as a fully sovereign state in a rule-based global order, rather than remaining a Russian satellite.

In 1994, the United States, Russia and Britain signed the Budapest Memorandum, laying out the crucial conditions for a peaceful post-Cold War order. This agreement contained an ironclad commitment to preserving Ukrainian sovereignty in exchange for Ukraine handing over all its nuclear weapons to Russia. It appears that at side meetings, American diplomats informed the Russians of the United States’ eventual plans to extend NATO to former Warsaw pact countries. The Russians grudgingly assented but drew their own redline: no NATO or European Union expansion to Ukraine.

Russian concerns about NATO enlargement and E.U. expansion came to a head in 2014 when pro-Western Euromaidan protesters ousted pro-Russian Ukrainian President Viktor Yanukovych. The protesters waived E.U. flags and clamored to join NATO. Acting out of what he perceived as defense, Putin sprang into action, invading Eastern Ukraine (the Donbas region) and annexing Crimea. Since that point, atop Putin’s geostrategic wish list has been the entry into the White House of a president who would condone Russia regaining its “traditional” hegemony over Ukraine.

The historical importance of Ukraine, however, explains why securing a pro-Western government that regains sovereignty over Crimea and the Donbas must be the United States’ top geostrategic goal abroad. More than any other international hot spot, the future of Ukraine can fundamentally alter the power balance at the heart of the Eurasian landmass.

Russia’s policies reflect this underlying truth. Ukraine’s economy is not only deeply intertwined with Russia’s — Ukraine is a key consumer and primary conduit through which Russian gas flows to Western Europe — but it also has a totemic importance in the psychology of Russians. Slavic civilization and the Russian Orthodox Church started with the Kievan Rus. Mother Russia was born in Ukraine.

This is the history lesson that Democrats must teach the American public. Simply put, Ukraine is the most important piece on the chessboard of geopolitics. And it always has been.

Until the American populace is convinced that Ukraine is truly our top geopolitical concern, Republican talking points about how there may have been a quid pro quo or how Trump exercised bad judgment on a phone call with Ukraine’s president will continue to convince many.

Understand Ukraine’s strategic importance, however, and it becomes clear that Trump’s conditioning of security assistance to Ukraine on investigations was not merely a quid pro quo or attempted bribery. It fundamentally traded away the United States’ most sacrosanct national security objectives in an attempt to advance Trump’s personal political ones. This is what members of Congress must hammer home, because it’s the key to comprehending the gravity of Trump’s alleged high crimes.