I believe this is garlic mustard. The first photo looks more like garlic mustard than the other two and there are a few look-alikes, so I can't be sure. But one way to tell for sure is to crush a leaf and smell it. Garlic mustard will have a garlic-onion smell.

Garlic mustard is an invasive plant:
http://www.dnr.state.mn.us/invasives/terrestrialplants/herbaceous/garlicmustard.html

Another Master Gardener has said he doesn't think it is garlic mustard. If you could verify whether it is or isn't by smelling as I suggested, and, if it is not, send me a photograph of the flower (it looks like it is about to bloom), I'll give it another try.

 I checked the plant and it does not smell like garlic. I realized the photos I took were not that clear. So, I cut one off and brought it in the house to take better photos.  Here is a better photo of the close-up of the top. The flower looks more like  tendrils, at least right now.   I have some other photos showing a close-up of the leaf and stem, too, if you need to see more.  Thank you so much for taking the time to look at this! 

 I checked the plant and it does not smell like garlic. I realized the photos I took were not that clear. So, I cut one off and brought it in the house to take better photos.  Here is a better photo of the close-up of the top. The flower looks more like  tendrils, at least right now.   I have some other photos showing a close-up of the leaf and stem, too, if you need to see more.  Thank you so much for taking the time to look at this! 

 Here is a better close-up of the flower  Plus the entire plant laid out on my table. 

Several of us have looked at this plant and I'm afraid we've not got a definitive answer. One suggestion was helianthus 'lemon queen':
http://www.oakleafgardening.com/plants/helianthus-lemon-queen/

In any case, I'd pull it. If you want a better answer, let one plant flower so you can see all stages of development. But don't let it go to seed.

Hi Dennis. Thank you so much for this response! I had gone away for four days and when I came back, lo and behold, there was a flower starting to open. I did shoot a photo of it, however, I do believe it has not fully opened.  I would love to send you a final photo of the flower fully open, if you don't mind.  It seems that this may be something interesting! It sure is a mystery. I can't thank you enough for taking a look into this.  Here are a couple new photos and I will send more when the flower is fully open. Thank you so much! 

Ah yes, that clarifies it greatly. It appears to be a campanula, although I'm not sure of the species or variety:
https://www.minnesotawildflowers.info/search?kw=campanula

You may have to wait until the flower opens to get a better read on the variety. In answer to your original question, it may be a cultivated variety, but campanula is native to North America:
https://en.wikipedia.org/wiki/Campanula

Native campanula (C. americana) is a good butterfly and bee plant.