The second Democratic presidential debate is upon us, which can only mean one thing: The 20 candidates hoping to boot President Trump out of office will be fighting for airtime and desperately searching for momentum before the lights go out at campaign headquarters.

But this debate shouldn’t just be about healthcare reform, immigration and ICE, Trump’s personality, and mandatory minimum sentencing. There are very serious developments happening outside U.S. borders. The contest for president is also a contest for commander-in-chief. There is a tendency for foreign policy to change the entire course of a presidency. Just ask George W. Bush.

Here are some of the most important foreign policy questions all presidential candidates will have to answer — if not on Tuesday and Wednesday night, then eventually.

1. What will you do about Afghanistan? Remember Afghanistan? Yes, roughly 14,000 U.S. troops are still on the ground in this Central Asian country advising an Afghan government that is about as corrupt and internally divided as it was five, 10, and 15 years ago. The war has cost U.S. taxpayers over $740 billion, a significant chunk of which has been spent on pie-in-the-sky reconstruction projects that either failed to be completed, were destroyed in the fight, or were overrun by quantum amounts of fraud and abuse. Trump reportedly wants to draw down the rest of the troops by 2020, peace deal or no peace deal. What will you, Candidate X, do about a war 59% of Americans and 58% of veterans believe is not worth the trouble?

2. Extend or not extend New START? Arms control is not exactly exciting for most people and may not even be on the radar of many of these candidates (to her credit, Sen. Elizabeth Warren is the outlier). But it should be. The Intermediate Range Nuclear Forces Treaty will die in the first week of August. The only nuclear agreement keeping the United States and Russia from engaging in another arms race is New START, which capped the number of warheads and deployed launch vehicles both countries can operate at any given time. If the treaty is not renewed by February 2021, the pact will go extinct, taking a half-century-long U.S.-Russia arms control regime with it.

Trump wants to hold out for a more comprehensive agreement and bring China into a trilateral discussion with the Russians, something Beijing has adamantly rejected. Is the Trump administration right or wrong? And if it’s wrong, what would you do differently?

3. On Iran, deal or no deal? On Iran, Trump has invested in a maximum pressure strategy that is falling flat. The White House objective is to squeeze the Iranian economy so hard that Tehran will come back to the negotiating table begging for a new deal. The president’s calculations have totally backfired; Iran is responding to what it regards as a U.S.-orchestrated “economic war” not by throwing up its arms and capitulating, but by sabotaging oil tankers in the Persian Gulf and slowly enriching more (and slightly higher-grade) uranium.

Assuming the situation doesn’t get appreciably worse by the time January 2021 rolls around, how will you attempt to get Tehran back to the table? What is your strategy to stabilize a bilateral relationship which has been weighed down by mutual suspicion from the start? Would you unilaterally reenter the U.S. into the Iran nuclear deal? Would you authorize preconditional diplomacy with Tehran, including at the senior levels of government or settle on a carrot-and-stick strategy? If an agreement isn’t possible, what would be your Plan B?

There are many other questions the moderators could ask. But these three are a start.

Daniel DePetris (@DanDePetris) is a contributor to the Washington Examiner's Beltway Confidential blog. His opinions are his own.