What’s worth fighting for against Russia or China?

Last Monday, in a single six-hour period, NATO launched 10 air intercepts to shadow six separate groups of Russian bombers and fighters over the Arctic, North Atlantic, North Sea, Black Sea and Baltic Sea.

Last week also brought reports that Moscow is increasing its troop presence in Crimea and along its borders with Ukraine.

Joe Biden responded. In his first conversation with Ukrainian President Volodymyr Zelensky, Biden assured him of our “unwavering support for Ukraine’s sovereignty and territorial integrity in the face of Russia’s ongoing aggression in the Donbass and Crimea.”

Though Ukraine is not a member of NATO, and we have no treaty obligation to fight in its defense, this comes close to a war guarantee. Biden seems to be saying that if it comes to a shooting war between Moscow and Kiev, we will be there on the side of Kiev.

Last week, Kremlin spokesman Dmitry Peskov answered that if the U.S. sends troops to Ukraine, Russia will respond.

Again, is Biden saying that in the event of a military clash between Ukrainians and Russians in Crimea, Donetsk or Luhansk, the U.S. will intervene militarily on the side of Ukraine?

Such a pledge could put us at war with a nuclear-armed Russia in a region where we have never had vital interests, and without the approval of the only institution authorized to declare war — Congress.

Meanwhile, off Whitsun Reef in the South China Sea, which Beijing occupies but Manila claims, China has amassed 220 maritime militia ships.

This huge Chinese flotilla arrived after Secretary of State Anthony Blinken put Beijing on notice that any attack on Philippine planes or ships challenging Beijing’s claim to rocks and reefs of the South China Sea that are in Manila’s exclusive economic zone will be backed by the U.S.

Our 70-year-old mutual security treaty with Manila covers these islets and reefs, said Blinken, though some are already occupied and fortified by China.

Apparently, if Manila uses force to assert its claims and expel the Chinese, then we will fight beside our Philippine allies. This amounts to a war guarantee of the kind that forced the British to declare war on Germany in 1939 over the invasion of Poland.

Two weeks ago, 20 Chinese military aircraft entered Taiwan’s air defense identification zone in the largest incursion yet by Beijing over the waters between Taiwan and Taiwan-controlled Pratas Islands.

While China appears clear about its aims and claims to virtually all of the islands in the South China Sea and East China Sea as well as Taiwan, it is less clear about its intentions as to when to validate those claims.

As for the U.S., does the present foggy ambiguity as to what we may or may not do as China goes about asserting its claims serve our vital interests in avoiding war with the greatest power on the largest continent?

If red lines are to be laid down, they ought to be laid down by Congress. And questions need to be answered to avoid the kinds of miscalculations that led to horrific world wars. For example, are the reefs and rocks the Philippines claim in the South China Sea, claims contradicted by China, covered by the U.S. mutual security treaty of 1951?

China is forcing America to address questions we have been avoiding for about as long as we can.

China is saying that it is not bluffing: These islands are ours!

Time to show our cards.