Run/walk through treacle

"Treacle" is a thick, sticky dark syrup made from partly refined sugar; molasses. It is something that would be very difficult to walk through and is therefore a metaphor for something that slows progress.

"Last week everything was easy and we were making good progress, but now it is like walking through treacle"

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"Trying to organise my new visa is like trying to run through treacle. It is taking so long!"