– President Trump doesn't appear to be heeding calls to end his rhetoric in regard to North Korea. In a pair of tweets, he boasted about America's nuclear prowess. "My first order as President was to renovate and modernize our nuclear arsenal," he tweeted. "It is now far stronger and more powerful than ever before." He then added, "Hopefully we will never have to use this power, but there will never be a time that we are not the most powerful nation in the world!" Earlier, in response to North Korea's threat to strike Guam, Trump retweeted a Fox News story about US Air Force jets taking off from Andersen Air Force Base in Guam for a training mission, with a caption noting pilots could be ready to "fight tonight," notes the Wall Street Journal. Related: Ad-lib? The New York Times reports that Trump's "fire and fury" line from Tuesday was improvised. The newspaper says the president did not run the language by advisers in advance, including chief of staff John Kelly. A piece of paper Trump had in front of him was reportedly a fact sheet on the opioid crisis. Politico reporter Josh Dawsey's sources tell him the words were not "carefully vetted," adding, "Don't read too much into it." Mattis weighs in: Secretary of State Rex Tillerson may have had a more calming tone on the subject Wednesday, but defense chief James Mattis followed up with some tough language. Among other things, he warned in an afternoon statement that North Korea should "cease any consideration of actions that would lead to the end of its regime and destruction of its people," per CNN. American nukes: Trump's tweets on the US arsenal were apparently in reference to a review of nuclear weapons that was ordered on Jan. 27 but isn't expected to be completed until year's end, reports the Washington Post. Such reviews are required by Congress about every eight years. After the last one in 2010, Barack Obama announced a $1 trillion plan to upgrade the nuclear arsenal over 30 years. Given all that, fact-checkers are pushing back on Trump's boast that he beefed up the arsenal, and that's putting it mildly. JFK comparison: “These are the moments when we have to come together as a nation and support the executive,” White House aide Sebastian Gorka said on Fox News, per Mediaite. “Whether you voted for him or not, whether they’re a Democrat or whether they’re a Republican, these are trying times. … During the Cuban missile crisis we stood behind JFK. This is analogous to the Cuban missile crisis.” Seeking ambassador: No ambassador to South Korea is in place yet under the new administration, and BuzzFeed reports that the absence of one is especially troubling now.