What is needed for hardware would be several large ion motors with fuel placed in solar orbit ready to be moved to and attached to any incoming body of import so as to nudge its orbit out of the way at an early moment and without the necessity of calling a special session of Congress or the General Assembly or causing stress to the industrious farming people of earth and their animals.
Wholeheartedly agree with your choice of engine. But the way to bump the interloper is to attach the engine to smaller (but still substantial) body, and use that to whack it. Of course, that capability will be frowned upon, from the political standpoint, because it can easily be weaponized. Using smallish asteroids to destroy cities is easier and cheaper than building a nuclear program, and the result can look like an act of nature.