Your intro should always and only include background info then say "this essay will discuss..." and repeat your title. For Johnson you need to include a bit about him in the first paragraph as background then break down the essay into paragraphs. Aim for six pages. Seems impossible but it's really not. Start off with he policies, give them a paragraph each. So, thats one on his great society, civil rights act and voting rights. At the end of each of your paragraphs you should reference the title, so always say if it was a success or failure blah blah blah. Your next paragraphs should focus on him getting involved in vietnam, him bombing, opposition growing back at home with resulted in his approval rating dropping and finally his resignation.