John McCain suspended his campaign in 2008 . . . to go to Washington to vote for bailouts which Bush engineered and Obama also voted for at the height of the financial crisis, making himself abhorrent to his free-market base and indistinguishable from his opposition at the same time. But it wasn't his signature issue.
Mitt Romney was caught telling a fundraiser in 2012 that 47% of the country, "the takers", weren't going to vote for him anyway, so forget 'em, which simply reinforced his image as "not really one of us" among the base, many of whom were in fact part of the 47% and at the same time people whom Romney had fired. But it wasn't his signature issue.
Donald Trump's signature issues have been illegal immigration and law and order, and there's no way in HELL forgiving immigration lawbreaking can be combined with law and order. Either all the laws are enforced, or eventually none of them will be obeyed.
Trump should have such a comprehensive view of that by now, but obviously doesn't, which means there's no there there.
The damage done thereby to the perception of Trump as a strong leader is incalculable.