Looking at Politico Article from March, a month or so after the appointment of Barr as Attorney General, it seems likely that the re-emergence of "Lock Her Up" is linked to the same drain the swap narrative used by the Trump campaign in 2016. I expect if he's ever asked about it directly he'll lay blame on Democrats for blocking investigations into Hillary Clinton.
The opening paragraph;
President Donald Trump said in an interview that aired Friday he hopes Attorney General William Barr will “do what’s fair” with regards to opening investigations to perceived crimes by his 2016 opponent Hillary Clinton, former FBI Director James Comey, former intelligence chief James Clapper and former CIA Director John Brennan.
This plays into Trumps repeated comments about the Russia investigation as a Witch Hunt and the "Crooked Dems" positioning. By suggesting he's asking for "fairness" it paints anyone who disagrees with him as "unfair". Given the Democrat control of the house of Representatives and the subsequent difficulty of a Republican President to promote their own agenda it seems likely this will build toward the same plan as 2016.