While I am concerned about immigration policies that enable followers of radical Islam to take root and establish Muslim communities under Sharia law in this country (e.g. in Dearborn, Michigan), by far the biggest threat to the greatness of the United States is the proliferation of lukewarm Christianity!
In Revelation 3:14-16 Jesus tells the church in the city of Laodicea that, because they are lukewarm (neither hot nor cold), He would spew them out of His mouth. This is because lukewarm Christianity does more harm than good. It lowers the standard of the faith so the norm becomes a dispassionate, nominal Christianity that has more in common with ungodly worldly systems than it does with biblical faith.
When a community in America is becoming dominated by Islamic principles it is the church in that community that is at fault since the church is the only entity with a mandate to become the salt of the earth and the light of the world. Thus, if Islam is spreading in a community, the church responsible for that particular community is no longer shining the light necessary to dispel the darkness.
When I view American history, I do not blame our country’s moral decline on the judiciary, politicians, academia or religions like Islam, Mormonism, and the like. I put the blame squarely on the lukewarm state of the average believer and the local churches that alone have the calling and capacity for bringing total transformation to a nation.
Consequently, the real problem is not that the world is getting into the church but that the (Laodicean) church has been getting into the world! The church has abandoned politics, economics, the sciences, biblical civic law, and the biblical worldview for a theology of escape that has stamped out our light in all the major components and mountains of culture and society!
Today, more churches are struggling for survival than ever. I believe the church is being tested as never before because God is separating the self-centered Laodicean church from the remnant (e.g. the church of Philadelphian in Revelation 3:7). In many cases local churches are a mixture of committed and lukewarm Christians, thus presently resulting in a national (perhaps global) purging in which thousands are leaving committed churches for either a church or a lifestyle of ease without biblical standards of accountability. This immense time of testing may even result in numerous local churches and ministries closing down!
In closing, Satan has no authority to close local churches. Jesus makes it clear in Matthew 16:18 that the gates of hell cannot prevail against His church. The only one in the business of closing local churches is the Lord Jesus Christ, who said that if we did not repent He would remove our lampstand (Revelation 2:5) and even make war against purported believers (Revelation 3:16)!