A “second betrayal” is the phrase being used on Taiwan to describe the lack of American pushback against Communist China’s intimidation raids. When the island democracy’s foreign minister “waved goodbye” as Speaker Pelosi’s airliner “taxied off into the sunset,” the Financial Times reports, it “evoked memories of the last US military commander’s departure in April 1979,” when America dropped Taipei for Beijing.

The year 1979 was, in the parlance of this crisis, the “first betrayal” — the American withdrawal from its defense treaty with the Republic of China and the diplomatic derecognition of its government, which was about to become China’s only democracy. It was done by President Carter in exchange for relations with the most tyrannical Chinese regime in all of history, the People’s Republic on the mainland.  Will it happen again?

“Immediate and dramatic” are the words the Financial Times is using to describe the Chinese response to Mrs. Pelosi’s visit. “Our firepower covers all of Taiwan, and we can strike wherever we want,” an official at China’s Navy Research Institute crows. Concerns are growing, at Taipei and Washington, that the high-level visit has “given Beijing the chance to demonstrate its capacity for military coercion,” the Financial Times reports.

The scale of the Chinese military exercises — being written up as a “rehearsal for a blockade” of the island — leaves “Taiwan even more exposed to the expanding rivalry between the two superpowers.” The show of force could scare off other European and Asian governments from supporting Taiwan. Witness, already, the refusal of South Korea’s president to meet with Mrs. Pelosi during her visit there last week.

The skittishness is understandable in the absence of a clear sense of whether America will step in to defend even a staunch ally like Taiwan. An ex-Portuguese European affairs minister, Bruno Maçães, points to China’s announcement that it will begin regularly conducting drills on the eastern side of the Taiwan Strait. “China militarises the strait, the US does nothing,” Mr. Maçães observed on Twitter, noting it isn’t “a well thought-out plan.”

The Chinese commissars, Reuters reports, now call the median line in the Strait, which is considered international waters, an “imaginary” boundary. America’s response has been to summon Beijing’s ambassador for a scolding. This is hardly likely to inspire respect from the “wolf warriors” of the Communist Chinese diplomatic corps, or confidence among other nations looking for leadership in the region.

No wonder the talk at Taipei is of a “second betrayal.” When it happened before it “left Taiwan isolated on the international stage,” the Financial Times writes. At the time, the Wall Street Journal lamented that America had “paid a high price in conceding the People’s Republic’s claims to Taiwan with so little assurance of Taiwan’s security.” Mr. Carter let the People’s Republic say that Taiwan had been “returned” to the motherland.

And, the Journal warned, with no guarantee “reunification will not be attempted by force.” A later Journal editorial warned that this was “not the way a great power should behave.” It stressed that the president’s actions were taken in defiance of the Congress. The Senate had voted 94 to zero to require that the Senate be consulted before breaking America’s defense pact with Taiwan.

Despite the betrayal, after 1979 Taiwan pulled itself up by its own bootstraps, reformed its governing institutions, and launched a free-market “economic miracle” that, the FT reports, transformed the island nation “into one of Asia’s most vibrant democracies.”  Today the mood is “starkly different.” A Taiwanese official says: “We have been working so hard to make Taiwan better. But right now, it is difficult to be optimistic about the future.”

Even President Trump, it appears, seems to be going weak on this head, as our Eli Lake observes today. In remarks at CPAC, he decried Mrs. Pelosi’s visit for giving Red China as “an excuse to do whatever they are doing.” Mr. Trump looks to be placating members of his party who envision America playing “a more modest role on the world stage,” Mr. Lake says. It’s hard to see the logic of that for America, Chinese democracy, or the GOP.