THE economy is sluggish but improving. President Obama’s approval rating is mediocre but not disastrous. Memories of Mitt Romney’s unsuccessful presidential campaign are relatively fresh . not least because Romney popped up briefly to remind everyone of them. And the Republicans pondering a run for president in 2016 all seem to sense that they need do to things a little, well, differently if they expect to ultimately win.

Maybe that means talking more about inequality . even putting it right in the heart of your economic pitch, as Jeb Bush seems intent on doing. Maybe it means trying to reach constituencies (young, black, Hispanic) that the Romney campaign mostly wrote off, which is what Rand Paul thinks his libertarian message can accomplish. Maybe it means projecting the most Middle American, Kohl’s-shopping, non-Bain Capital image possible . which is why the recent media fascination with Scott Walker’s lack of a college diploma was probably a boon to the Wisconsin governor.

When it comes to the Republican Party’s basic presidential-level problem, though . the fact that many persuadable voters don’t trust a Republican president to look out for their economic interests . it should be easy to tell whether the way a candidate differentiates himself will actually make a difference. Just look at what he proposes on two issues: taxes and health care.

These are obviously not the only domestic policies worthy of debate. But they’re two places where the immediate link between policy and take-home pay is very clear and two places where abstract promises about “opportunity,” “mobility” and “the American dream” either cash out or don’t.

Precisely because there’s real money on the table, they are places where being a reformer requires more than lip service. One reason issues like immigration and education are appealing to Republican politicians looking to change their party’s image is that policy change in these areas seems relatively cheap . more green cards here, new curricular standards there, and nothing that requires donors and interest groups to part with their favorite subsidies and tax breaks.

But you can’t reform the tax code or health care that easily, which is why those issues offer better, tougher tests of whether a would-be conservative reformer should be taken seriously.

Not coincidentally, they’re policy tests that Obama-era Republicans have often conspicuously failed. On taxes, the party has been enamored of reforms . some plausible, some fanciful . that would cut taxes at the top while delivering little, or even higher taxes, to most taxpayers. (It’s an odd position for a party that is officially anti-tax to take in an age of wage stagnation, but at least the donors have been happy.) On health care, the G.O.P. has profited from the unpopularity of Obamacare, but we are now at Year 6 and counting without anything more than the pretense of a conservative alternative.

These failures have not been for want of policy options; they’ve been for want of ingenuity and will. The list of plausible conservative health care alternatives now literally fills a book . “Overcoming Obamacare,” from The Washington Examiner’s Philip Klein, which any G.O.P. presidential contender would do well to at least pretend to have read. The best of these alternatives would allow a Republican candidate to promise, as Romney did not, to mostly maintain Obama’s coverage expansion (albeit with less comprehensive coverage) while lowering health insurance premiums for most Americans.

On tax policy, similarly, several obvious avenues are open to a would-be reformer. One possibility is the family-friendly tax reform championed by Senators Marco Rubio (the presidential contender with the strongest policy agenda to date) and Mike Lee, which would deliver substantial tax relief to families with children. Another is a straightforward payroll tax cut, which would raise take-home pay for existing workers and reduce the cost of hiring new ones.

But again, these kinds of policies cost money. A plausible Obamacare alternative requires a tax credit for purchasing insurance; a middle-class tax cut requires, well, a middle-class tax cut. If you want these things, you probably can’t have certain other priorities beloved by the party’s donor base . like, say, the lowest possible top marginal tax rate.

So embracing reforms that deliver something tangible to middle-class voters means embracing a policy fight.

But Republicans who decide to duck that fight won’t really be tackling Middle America’s biggest challenges . or their party’s biggest political problem.

If Jeb Bush decides that his big reform ideas will be immigration and the Common Core, his “right to rise” rhetoric will be mostly empty. If Scott Walker campaigns on, say, a flat tax and restoring the pre-2009 health insurance status quo, his middle-class shtick will remain just that.

But if the party nominates a candidate who offers something genuinely different on these issues than his predecessors did in 2008 and 2012, the possibility of a different general-election outcome might be there for the taking.