I'd remind people that Reagan wasn't just a conservative. He had a very positive message about America's future.
I don't think a conservative with a negative message can win, no matter how conservative.
I agree. Bush, too, famously projected himself as a "compassionate conservative". Before that, folks like Jack Kemp applied conservative concepts to the abatement of poverty, or the encouragement of enterprise in poorer communities. Bush helped carve a role for partnership with religious organizations with educational or mercy missions.
Back in the day conservative thinkers advocated competition with public education, the reform of welfare, and the use of private insurance to address the access crisis with respect to healthcare financing. Romneycare was the product of conservative policy thinking.
The TEA party changed the focus of conservatism from encouraging enterprise and growth to reducing the size of government. That may be laudable, but it's a hard sell politically. But Trump bears no relation to the TEA party. Trump's promoting an activist "conservatism" (I'd say proto-fascism); he certainly has no intention to reduce the size and role of the Federal government.
But Trump is pushing a negative activist "conservatism", as compared with the positive activism of Reagan, Bush and Kemp. He's going to kick people out, he's going to stop the brown invasion. (Of course, a lot of considered folks think that crap's an affront to values that include, among other things, conservatism, but that's why the GOP is cracking up (or, I'd argue, being hijacked.)