What does Reagan's joke about three dogs mean?

On one occasion, Reagan wanted to make a radio address to the whole country. Before the official speech is about to begin, the studio staff are making final preparations. "Mr Reagan, please try stereo again. It will be officially broadcast in a few minutes. "

Reagan sat in front of the microphone and said in a solemn voice, "American citizens, I am very happy to tell you that today I signed a decree to destroy Russia." In five minutes, we will start bombing Russia. "

As soon as this sentence was finished, the studio immediately went haywire. Some people suspect that there is something wrong with the stereo, while others think that there is something wrong with the ears. A staff member asked trembling.

"Mr. President, you didn't officially announce it, did you?"

"Of course not, it's just a joke, just like 9, 8, 7, 6, 5, 4, 3, 2, 1."

"There are two minutes left. Don't you want to try again? "

"I don't want to try."

"Please try again anyway?"

"Why?"

"Now many people in the sound room have put down their jobs and gone out to call their wives."

"What the hell happened?"

"They want to tell their families that they are going to Russia early."