Okay, Clay's successful reelection bid in 1844 is seen by many as THE pivitol event in the history of the United States, and rightfully so. But what if the Democrats win (you could keep Polk as the candidate, or find someone you think would have a better shot). Here are the issues I would like to discuss.
1) Is there US Civil War still happen, and if so, when? This is obviously the big one, as Clay's reelection and his refusal to annex Texas is what led to the slave states attempting to secede. I figure the free and slave states were bound to come into conflct sooner or later, but it could take place in thre 1850's or 60's, and obviously with a different causus belli.
2) How does slavery come to an end in the US (if indeed it does)? At the conclusion of the Civil War, President Clay came up with the plan to phase out slavery in 20 years, with the slaveowners being compensated for emancipation. The plan was of course seen by many northerners as being far too lenient on the seccessionists, but many others credit the plan for avoiding unrest in the South after the war was over. Is there another way for emancipation to play out.
3) Will there still be an Oregon War, or will Britain and the US manage to compromise on the boundary dispute? The US couldn't (or wouldn't) deal with the issue until the Seward Administration in our world, but with them possibly avoiding the Civil War, they would have a lot more energy to focus on the issue (indeed, it would be a useful way to channel the probable north-south tensions). And if war is unavoidable, would the result change?
4) How would Winfield Scott be remembered today? We tend look at him as the greatest general in US history, but a lousy President. But without a Civil War to be fought, he probably doesn't win the election in 1848, (and lose badly in 1852).
5) How would Texas develop as part of the US instead of an independent nation? This was after all the Democrat's big issue against Clay. Despite being proud of it's fiercely independent nature, it's had to do a difficult balancing act between Mexico, the US and Great Britain to retain independence. (It only gave up legal slavery in 1870 due to the three countries all putting pressure on it, though blacks continued to serve in slavery like conditions for decades afterward). Would the slaveowners fleeing the US government have anywhere to run to?