I've read several of his articles that were linked on various Christian websites and he has a habit of quoting scriptures completely out of context and thereby writing articles that are not scriptural in any sense.
However, the point of this article, from near I can tell, is that "No," we can't pray for a nation's salvation because the process of salvation is a personal experience, not corporate or national.
Yes, no, maybe?
Based on the Scripture in the article, each individual has to choose to accept Christ for himself. And it would appear that once God has decided to send judgment on a nation, the prayers of the righteous will not help that nation.
I see it more as him saying that we can't repent of national sins, the sins of others besides us, and expect God to refrain from judging the US because of it.
I think we desperately need to pray for the salvation of souls in this country, and we do need to pray for godly leadership, and righteousness to prevail, because we are commanded to. Whether it's going to have any effect is another matter. But our praying is a matter of obedience, whatever the outcome.
In church today, our pastor prayed for obama for his salvation and for him to make good decisions that would turn the direction this country is going in.