Really, with all the important issues that should occupy a president's attention, if this is even on your radar, you're not qualified for the job.
Converting to metric is not just a fun science nerd issue no one cares about.
Really it's an economic issue, and I'm surprised it hasn't been made more of a big deal. When we follow international standards, we can better share ideas and better trade goods. If the US used metric, we'd be in a much better position to sell our goods worldwide, as we wouldn't need to re-tool or re-calculate all the time.
Great example: our US engineers are mostly trained in the English system. My wife used to work in an industry that is now heavily developing and building things overseas. The American engineers had to build everything to metric standards, since they were building in India and what not, and really had trouble with it, as they weren't properly trained to do metric calculations and the equipment they wanted to buy from American companies didn't always come in a metric size. Instead, the engineers would have to half-ass some crazy scheme (like buying parts and then cutting them -- makes sense until you realize you'd have to pay field guys to do this 10,000 times) to get it to work. The quality suffers, and since there's all these problems, I get the sense that many international companies would rather just hire Germans or whatever to do it.
This is an anecdote of one industry, sure, but if our engineers were trained in metric, and our businesses made the jump to make metric products in the first place, we'd probably be a lot more competitive in the world market. We wouldn't need to spend all this extra time and money on customization, we could just do it. I imagine all this effort has long ago exceeded the cost of buying new tools once; we should have just switched then and told businessmen to shut up about costs.
All of that absolutely doesn't matter. The US doesn't export cheap manufactured goods. We just don't do it. We're too high on the standard of living pyramid to make it work economically.
For expensive precision goods, I have yet to find a machinist who can hit a dimension of 4.000" +/- 0.001" but can't machine the same part to 3.937" (100mm). The machines all have toggle switches, but to reduce errors it is better to just have the engineer do all the conversions to inches right on the drawing or in the CAM program.