President Bush Jr. has never supported amnesty. President Reagan signed amnesty into law. But beyond those two, I'm not sure as to the positions on illegal immigration of prior Presidents. But I do know this: George W. Bush supported comprehensive immigration reform and won 40% of the Hispanic vote in 2004. Mitt Romney took a hard-line stance and won 27% of the Hispanic vote in 2012. Donald Trump's fiscally irresponsible, anti-5th amendment approach to this issue will cause him to lose the Hispanic vote by an even larger margin than Mitt Romney.
The bolded is untrue or unsound.
Bush Jr., who supported a pathway to citizenship, indeed won 40% of the Hispanic vote; and Romney, who opposed a pathway to citizenship, indeed won just 27% of the Hispanic vote.
However, you must also consider:
1). John McCain, who supported the same pathway to citizenship that Bush did, won a measly 30% of the Hispanic vote.
2). George Bush Sr., who helped write amnesty with Ronald Reagan, won around 25% of the Hispanic vote (worse than Romney).
3). Even Ronald Reagan during his landslide victories could only garner 35% and 37% of the Hispanic vote in 1980 and 1984, and he gave amnesty to illegal immigrants.
Clearly, you see that it's not that simple. Even if a GOP candidate supports amnesty, he or she is not guaranteed the Hispanic vote.