Last week at a rally in Florida President Trump again decried the impeachment inquiry launched after a phone call with.
Ukraines President Vladimirs Zalenski, in which Trump appears to ask for help investigating a political rival.
这是近期的美国之音的文章。
以上最后一句话，为何不说to investigat a political rival， 却说 investigating a political rival. 二者的差别在哪？
语法怎么样剖析？句意有什么不同？
《朗文》名词help使用方法：
help2●●●S1W1noun
1[uncountable]things you do to make it easier or possible for someone to do something
Thank you for all your help.
help with something/with doing something
Do you want any help with the washing up?
help to do something
I could do with some help to bring the bags in from the car.
help doing something
He asked for my help in getting an interview with her.
以上名词help使用方法表明，help既能够后接to do不定式，也可将来接in doing, 而且介词in是可以省略不需要的。所以，美国之音文章并没错。这里用 to investiggate 和 （in）investiating意义相同。
