Help me understand this sentence

[amateur]

"High-speed rail helped cost Democrats a special election for a state Senate seat this summer and a Congressional race last November, both in the Central Valley."
Source: WSJ http://online.wsj.com/news/articles/SB1 ... _&_outlook

I understand the meaning of the sentence on the whole. It says that high speed train caused the democrats loose a couple of seats. So when High speed train is singular why is cost used? This summer is not in the past so shouldn't cost be costs instead? Please explain.

[RonPurewal]

"High-speed rail helped cost Democrats a special election for a state Senate seat this summer and a Congressional race last November, both in the Central Valley."
Source: WSJ http://online.wsj.com/news/articles/SB1 ... _&_outlook

I understand the meaning of the sentence on the whole. It says that high speed train caused the democrats loose a couple of seats. So when High speed train is singular why is cost used? This summer is not in the past so shouldn't cost be costs instead? Please explain.

The verb is "helped".

This construction is identical to "helped to cost...". In practice, the "to" is often omitted.
No, GMAC won't test this.