Obama's at 43% right now on RCP average and fairly stable (he's been around 43-45 since last May). George W Bush was at 37% at this time in 2006 and tanking downward after starting 2006 in decent position. Completely different scenarios. Also, Americans still had faith in the opposition party. Neither party is well liked now.
The "Bush Sr lost 10% off Reagan" is not only poor logic but inaccurate. He lost 6 (59 to 53). Also, Bush was trailing Dukakis big in late 1987 and early 1988 as Reagan was around Obama's current 43%. Bush was always 3-4 points behind Reagan's approvals. Hillary is running 7-8 points ahead of Obama's approvals.
I said Bush Senior lost ten percent of the vote Reagan got.
Reagan got 54,455,472 votes in 1984.
Bush got 48,886,097 votes in 1988.
Bush got just under 90 percent of Reagan's 1984 vote. And that was in a fantastic year electorally.