Don't step over the line and remilitarize the Rhineland. Absorbing Austria would cross a red line. Breaking up Czechoslovakia is unacceptable. Get out of Poland by the announced deadline. The rest was history.
Don't dare blow up another American military barracks overseas. Don't ever consider another attack on the World Trade Center. Don't even try blowing up one more American embassy in East Africa. Don't ever put a hole in a U.S. warship again. The rest was history.
President Obama issued yet another one of those sorts of warnings to stop the violence to Ukrainian President Viktor Yanukovych just before protesters drove him out of office. "There will be consequences if people step over the line," Mr. Obama threatened.
Ben Rhodes, the president's deputy national security adviser, amplified that veiled warning. He called the Ukrainian government repression "completely outrageous" — as opposed to just outrageous or completely, completely outrageous.
Secretary of State John Kerry joined the chorus of condemnation by hinting at economic sanctions if Mr. Yanukovych didn't stop his violent crackdown on protesters.
Why does this rhetorical assault sound familiar?
During the last five years, Mr. Obama has issued serial deadlines to Iran to cease and desist from its ongoing enrichment of uranium. All the while, more Iranian centrifuges went online.
Later, Mr. Obama turned from deadlines to red lines. He threatened Syrian President Bashar Assad with one about using chemical weapons. "A red line for us," the president warned, "is we start seeing a whole bunch of chemical weapons moving around or being utilized."
Mr. Assad moved over that American red line, using chemical weapons to gas his own people, and is now winning the war against the Syrian insurgents. In the end, an embarrassed Mr. Obama was reduced to denying that he had never issued a red line in the first place: "I didn't set a red line. The world set a red line."
The administration's latest cry of "outrageous" does not seem so absolute, either. Remember, the president himself used that exact adjective to condemn the Internal Revenue Service scandal when it was revealed that the tax agency was inordinately focusing on conservative groups.
Later, after various key IRS officials had invoked the Fifth Amendment, resigned or abruptly retired, Mr. Obama brushed off the scandal. It was, he said, mostly a media event conjured up by "outraged" journalists. Somehow, a scandal that the president once decried as institutional abuse ended up as a media melodrama perpetrated by unduly outraged reporters.
Will the Ukrainian mess now abate due to Mr. Kerry's hints at sanctions?
Given Mr. Kerry's loud global-warming sermonizing and the administration's serial threats, bad actors abroad probably believe that burning too much coal is more likely to anger the United States than shooting protesters or gassing enemies.
After the Obama administration finally assembled a coalition of allies to impose tough sanctions against Iran, and after the trade embargoes began to bite the theocracy, Mr. Obama, without warning his coalition, abruptly relaxed those embargoes and entered into talks with the Iranians.
The message? Imposing sanctions is a difficult business. When they finally work, they are likely to be abruptly lifted if the squeezed nation sends out a few peace feelers and wants to feign appearing reasonable.
The United States has now shot so many rhetorical arrows that its quiver of indignation is empty — and the world's troublemakers may know it. An administration that ignores almost all of its own Obamacare deadlines surely cannot expect others to abide by any timetables it sets abroad.
There may be no viable solutions to the violence in Syria or Ukraine. The messes in Egypt and Libya, the Chinese provocations to their neighbors, the North Korean lunacy and the spiraling violence in Venezuela certainly have no easy answers. Not knowing quite what to do is not the same as knowing certainly what not to do.
Although the United States alone seems to honor its promised deadlines of withdrawal from Afghanistan and Iraq, the world's aggressors sense that the Obama administration's bluster is predictably to be followed by more bluster. Therefore, they have decided to risk aggrandizements while they can. In the mind of Vladimir Putin, today Ukraine, tomorrow the Baltic States or Eastern Europe. For the Iranian theocrats, if chemical weapons are OK in Syria, why not nuclear weapons in Iran? For China, when Japan backs off, why shouldn't Taiwan, South Korea or the Philippines?
Such a seemingly insignificant loss of deterrence is how wars often start — when an aggressive nation bets that loud words signal that consequences will never follow. So it is emboldened to up the ante and try something even riskier.
America's outrage over deadlines and red lines is long past monotonous and empty — and the result has been an ever scarier world.
Victor Davis Hanson is a classicist and historian for the Hoover Institution at Stanford University.