A wild goose chase

doing something that may seem impossible, meaningless or pointless

Giving cold shoulder

to ignore someone

Clouds on the horizon

trouble is coming on the way

Let someone off the hook

to let go someone, to not punish or hold someone responsible for something

Feeling under the weather

not feel well; feel sick

Cutting corners

trying to save money or time, by not performing duty or the given task; to skip steps or not do things completely

Go down in flames

to fail in a surprisingly manner

The last straw

the difficulty that ultimately makes the situation worse or unbearable

Break the ice

to get the conversation going

Wrap one's head around something

to understand something that may take a bit of time and effort

Burn bridges

to do something or anger someone to where you cannot go back to how things were and cannot expect help in the future

Your guess is as good as mine

I don't know either

Leave out in the cold

to be ignored or not considered

Keep an ear to the ground

to listen for new information

Run around in circles

to put effort into something while making little or no progress

Scrape the barrel

to make choices you don't want to or normally wouldn't

Having an Ace up the sleeve

to have a hidden or untold advantage

Hook line and sinker

to be deceived completely

Bone to pick

to be angry about something and want to discuss it

Down for the count

to give up or not be able to keep going