Warrantless Wiretapping

The NSA’s (National Security Association) warrantless wiretapping controversy became a major issue when the war on terror started back in 2001. The Bush administration was in control and Bush had given consent to authorize warrantless wiretapping on phone calls, text messages, internet activity, e-mails, etc. in 2006. Congress passed the “Protect America Act of 2007" which is the act that legalized warrantless wiretapping.
Legalized? Really? I find that hard to believe (even though it’s a reality) that they can legalize an act of that stature. That is a complete invasion of our privacy, and is even stated that way in the Constitution. The Fourth Amendment of The Bill of Rights states, “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause supported by Oath of affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”
According to a few different reputable sources I read, the government has only admitted to eavesdropping on calls and e-mails where "one end was overseas and one person was suspected to be a terrorist." It has never officially confirmed that it sucked in the records of millions of Americans, despite repeated reports and confirmations from Congress. But there have been reports that make it clear that there were more intelligence programs that the so-called “Terrorist Surveillance Program” that the administration acknowledged after the New York Times revealed in December 2005. Also from what I’ve read, it’s apparently not that hard to get a warrant… It seems as if they (the government/police) wanted to put someone or some group under surveillance they would have some sort of probable cause that caught their attention, so why not use it and make this a legal process? All a warrant takes is probable cause! Why can’t the government or police just obtain a warrant first? In my opinion they should not be able to invade our privacy without a court ordered warrant which was collected from probable cause. I understand that the war on terror was a very serious issue, and that the Bush administration wanted to go to every length possible to catch the terrorists causing all the troubles and heartbreaks, but can’t they get a warrant first? What I want to know is, how much did this help in the search for terrorists? Also, how much has this invaded non-terrorists privacy and gotten them in trouble?
My only problem is that they are invading innocent people’s privacy, and that is illegal (or should be illegal). I guess it’s kind of one of those things where “one person can ruin it for everyone”. So until this becomes illegal again, looks like we all need to watch what we say wherever we are, and especially watch our jokes… Sad it had to come to this.