President Trump is the most powerful leader on Earth. But to influence global actors, he must ensure that his words carry credibility. And unfortunately, he is making too many threats that he's not delivering on.

Consider a few examples.

Earlier in the week, Trump was threatening to close down the border. Now Trump has abandoned that warning in favor of dangling tariffs on Mexican car exports. This policy change might be a good thing, as a border closure would damage U.S. businesses and consumers. But Trump should never have made that threat in the first place, because now, as with his recent threat to shut down the government unless Democrats appropriated money for his border wall, Trump has proven himself a blinker.

Another recent example comes in the area of healthcare. Trump this week abandoned his earlier plan to introduce a new healthcare replacement bill for Obamacare. Trump now says he meant that any bill would be introduced in 2021.

What about Venezuela? Trump and his top officials spent the first part of the year warning Nicolas Maduro that he would fall. Trump added that if Maduro arrested Venezuela's interim President Juan Guaido, it would spark serious U.S. reprisals. The implication was that these reprisals would involve Trump's use of U.S. military force. But now Maduro's escalation meets Trump's effective silence. The Russians and Maduro recognize it, and are doubling down against Guaido.

It's a similar story on North Korea. Trump spent 2018 pushing Kim Jong Un toward negotiations. But in 2019, Trump has abandoned any hint of toughness. Instead, the president makes one-sided concessions to the North Korean leader. Kim's nuclear and ballistic missile program remains alive and well.

All in all, Trump is weakening his credibility by constantly proving that what he says he'll do isn't indicative of what he will do. Thus, what Trump says might or might not mean anything. This weakens Trump's ability to negotiate effectively with Democrats, but it also undermines his negotiations with regimes like that of China. In 2019, Trump looks inherently malleable. That's a poor recipe for leadership.