tip, at the water's edge, bring to its knees
1 "This is really the year that mobile has tipped for consumers," says Alexis Rask, chief revenue officer for mobile shopping app start-up Shopkick, which gives users points for walking into partner retailers that can then be redeemed for gift cards and other prizes.
2 "There used to be a pretty important principle that originated in the Republican Party, I believe, that partisan politics should stop at the water's edge," said White House spokesman Josh Earnest. " And it's unfortunate that we did see a number of Republicans yesterday who criticized the president for a handshake at Nelson Mandela's funeral."
3 He was a guerrilla, the commander-in-chief of the ANC's armed wing. Umkhonto we Sizwe, which, as the " Spear of the Nation", was supposed- however implausibly-to lead an armed insurgency, organise an invasion by sea and bring the government to its knees.
What do these phrases mean in the sentences? Thanks