Large angular scale polarized microwave emission is key to probing both Galactic structure and cosmological phenomena. Polarized Galactic sources, including synchrotron, thermal dust, and potentially anomalous microwave emission, trace the Galactic magnetic field and the interstellar medium. A deeper understanding of the Galactic signal will aid in unraveling the polarized cosmic microwave background (CMB) through effective component separation. CMB E-modes at <20 offer strong constraints on the reionization optical depth, while B-modes potentially hold direct evidence of inflation through primordial gravitational waves. The Cosmology Large Angular Scale Surveyor (CLASS), located in the Atacama Desert of northern Chile, is a telescope array that surveys the sky with single-frequency-band telescopes centered at 40 GHz and 90 GHz, as well as a dual-band 150/220 GHz telescope. Ground-based observations face challenges in recovering large-scale information due to low-frequency 1/f variations from atmospheric, instrumental, and calibration drifts. CLASS maintains long-term stability via front-end polarization modulators. I will describe the design, fabrication, and performance of a new polarization modulator, the rotating reflective half-wave plate modulator, which nearly doubles the linear-polarization mapping speed of the 90 GHz telescope and helps us better understand systematic errors from the modulation step. I will also present an analysis of polarized synchrotron radiation based on CLASS 40 GHz and WMAP K/Ka/Q-band (at 23/33/41 GHz) data, featuring sensitivity-improved polarization maps at 40 GHz and the spatial variation of the polarized Galactic synchrotron spectral index. Finally, I will look ahead to forecast CLASS and LiteBIRD's potential to corroborate four large angular scale temperature anomalies of CMB. We found that the ΛCDM model predicts weak correlations between T-mode and E-mode statistical tests for anomalies, suggesting that future polarization experiments will generate independent measurements that may firm up the significance of the anomalies in temperature.

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