重点“could have ～ed“

重点“could have ～ed“  在英文里意思 you were able to do, but didn't do。 你能做，但(实际上)并没有做. 
唉，给你举个例 “You could have passed the test （=You were able to pass the test, but you didn't.  翻译：你（本或许能够）通过测试，但你（实际上）并没有通过)

而具体到那句“we are “72 hours into the diagnosis,” meaning the president could have tested positive as early as Wednesday”后半句是对“72 hours into the diagnosis,”的进一步解释说明，
意思是总统早在周三或许可检测出阳性，but the president didn't test。总统（实际上）并没有检测，假如若检测了其结果或阴或阳。医生推测，若周三做了检测结果可能会是阳性。就是说周三时并没做检测，更不要说确诊。

明白理解了没啊?   英文水平有待提高咯 :)  英文与中文是不同语言系统，语法和讲话思维也不同，直译会闹大笑话。