JAMES OLIPHANT and DOINA CHIACU THE Republican Party kicked off its convention to re-elect U.S Donald Trump with an unsubstantiated warning from the president himself that he may face a "rigged election," followed in the evening by full-throated praise for Trump and warnings that America would crumble under Democratic leadership. WARNINGS AMERICA AS WE KNOW IT WOULD DISAPPEAR Democrats spent much of their national convention last week trying to convince independent and even lifelong Republican voters that nominee Joe Biden would be an acceptable choice. The Republican approach has been much different. From speeches from the McCloskeys, the St. Louis…