Multiple observers have suggested that Trump is capable of enacting a “wag the dog” event, taking its eponym from the movie in which a presidential candidate fabricates a war to conceal a sex scandal. In the Trump version, the sex scandal, one of them anyway, is already public knowledge, he is president, and the war would be an actual war in which real people would die.
Given how amoral Trump and his toadies are, and how entirely he and his fellow Republicans subordinate all other considerations to getting and retaining political power for no discernible reason, it is far from implausible to think that Trump could start a war as a way to head off impeachment proceedings in the House of Representatives.
There is no legal reason why impeachment is impossible during war time, but politically, the president usually gets a huge upsurge in public support during any foreign policy emergency, even a manufactured one, so beginning impeachment when the nation is at war would be very difficult politically, especially when the leadership of the House is already operating under the misapprehension that impeachment threatens significant political risk.
Trump has two likely options teed up that could provide vaguely plausible excuses for starting a war, Iran and Venezuela. Venezuela looks more likely now, since the Trump administration is already on record as supporting the so far unavailing efforts of a challenger to the sitting president to depose that sitting president, Venezuela likely has less capacity to mount a serious military response, and being in the western hemisphere, invading there would be cheaper, not that Trump has any concern about wasting public funds (see border wall).
We know he also has no concern about disrupting people’s lives, even killing them, in pursuit of his noxious political program. Although he apparently feels quite secure at the moment, and likely is safe from removal because his partners in crime still control the Senate, still, impeachment could well drive him to some act of insanity.
Better to go ahead and force the issue, so that some benefit will accrue from any invasion, not a benefit the targets of the invasion will much care about or feel, but a benefit to the world in general that will flow from making a clear statement that the United States will not indefinitely tolerate a president as amoral, incompetent, and corrupt as Trump.