Nixon, in the newspapers that morning, argued that the crisis in the Middle East meant that Watergate had to be put aside; Henry Kissinger, that morning, flew to Moscow to negotiate the tense situation, and Nixon spoke about “those in the international community who may be tempted by our Watergate-related difficulties at home to misread America’s unity and resolve.”
This is a particularly egregious instance of a not-terribly-uncommon way of invoking the credibility fairy. The argument (which is not, itself, wholly insensible) is that domestic dispute produces international uncertainty with respect to American resolve and interest, undermining the credibility of U.S. commitments. The most common manifestation of this during the Bush administration was the effort to quiet Iraq critics by claiming that terrorists and insurgents drew inspiration from American discord. To my recollection we’ve seen a lot less of this particular trope during the Obama administration; while I recall plenty of arguments about credibility during the Syria debate, I don’t remember many claims that domestic disagreement itself undermined US resolve-itude. The closest we’ve come to a domestic-politics-as-credibility-problem lately is the debt ceiling fight, which is more about institutional capacity in the face of domestic political conflict than about resolve per se.