Question: How likely is a Bitcoin Shutdown via overloading the network?

 Hey guys, I was wondering: What if some government or some bank or some rich  guy got 2 bitcoin wallets and then just spammed millions of transactions  (or however many) per seconds from one to the other and vice versa? I  know the fees would quickly rise, but that could get paid, if you have  that kinda money. Couldn't the whole bitcoin network then be shut down  (or rather: jammed up) so that nobody could send or receive bitcoins. Is  there some mechanism that prevents that? Thank you for the info! :)