The phrase "a preview of how difficult" is correct and usable in written English.
It can be used when introducing an indication or glimpse of the level of difficulty that may be encountered in a situation or task.
Example: "The initial tests provided a preview of how difficult the final exam would be."
Alternatives: "an indication of the difficulty" or "a glimpse of the challenges".
As President Barack Obama rallied his reelection team back in 2012, he received a preview of how difficult it could be to make sure that strategists, spokespeople, and prominent supporters didn't sabotage his case against Republican opponent Mitt Romney.
And the conflict over the review findings is a preview of how difficult it could be to prove that trade center dust — a complex mix of materials created by the collapse of the twin towers — sickened workers.
Yet the executives offered little common ground about how to solve the problems they highlighted, and repeatedly clashed with one another during two and a half hours of testimony — giving lawmakers a preview of how difficult it may be to satisfy all parties in the rapidly evolving but fractious music market.
This is a preview of how your content will look on export.
Examining the Patient Protection and Affordable Care Act and existing pilot studies can offer a preview of how chronic care of spine pain will be sustained.
They were instead offered a preview of how a President Clinton would handle an act of terror on US soil.
We're already seeing a preview of how this will work in practice when Trump is president.
Members of the Senate Judiciary Committee are likely to signal their intentions at a hearing on proposed gun legislation on Thursday, offering a preview of how other lawmakers might vote.
For now, we have the stories collected in this volume, which give us a preview of how September 11th might look through a "speculative" lens.
A pretrial hearing also would provide prosecutors with a preview of how Mark O'Mara, Mr. Zimmerman's lawyer, plans to present his case.
Passbook, a new iOS app that was featured at the conference, appeared to offer a preview of how payments would actually be made.
